Popular HVAC Questions & Answers

On this page we have listed some popular questions with answers that our customer’s have asked us in their emails. I hope this will help answer some of your questions about heating and air conditioning. More questions and answer will be coming soon. If you have a question please email us anytime: support@arnoldservice.com We would love to help you out and have your business! Thank you so very much for visiting our website! One of my favorite quotes by David Jeremiah: “Nothing is more valuable than helping another person succeed!” We would love to help you troubleshoot and repair your furnace or air conditioner problem! Steve & Barbara Arnold

Popular HVAC Problems with Answers:

1. Customer problem: I am going through an ignitor almost every year. I think it is because my furnace to cycle off and on too much. What could be the cause for my furnace cycling too much?

Answer: Furnace short cycling is very hard on the furnace and hard on your energy bill. Furnace short cycling can be caused by (1) the thermostat anticipator (if equipped) not set high enough, (2) gas valve gas pressure set too high (too much gas coming into the furnace causing furnace to over-heat) (3) blower speed set too low or weak blower motor capacitor (4) duct work too small to provide enough air flow for the furnace, (5) evaporator coil stopped up with dirt or lint or (6) a furnace that is sized too large for your home. I hope this helps you find out why your furnace is cycling too much.

2. Customer problem: Why am I not getting 24 volts to the contactor on my air conditioner or heat pump? Where does the 24 volts come from?

Above picture of a transformer:

Answer: The 24 volts comes from the transformer. We sell transformers on the following page: Please click here to see the transformers we sell. Most of the time the transformer is located inside the furnace, although sometimes (about 10%) it is located inside the outdoor AC unit. The transformer produces the 24 volts which goes up to your thermostat then out to your air conditioning unit when the thermostat calls for cooling. I would suggest that you try to turn the thermostat down so the air conditioner is supposed to come on. Pull your high voltage disconnect so there isn’t a chance of you getting shocked. Test with a volt meter set to “Volts AC” and see if you are getting 24 volts straight out of the thermostat wires that come into your outdoor AC unit. There should be two thermostat wires that go into your AC unit. If you are getting 24 volts then probably one of your safety controls on your air conditioner is not allowing the contactor to kick in. A lot of the time air conditioning units have both high and low pressure (low refrigerant) switches on them. If you do not have enough Freon (refrigerant) in the system it will not allow the unit to come on. If you aren’t getting 24 volts straight out of the thermostat wires, then you could have a thermostat, transformer or wiring problem. Best of luck in finding the problem!

3. Customer Problem: My Air conditioner’s contactor will not engage. I am not getting 24 volts to the contactor to make it engage? What could be the problem?

Answer: If the contactor is not getting the 24 volts then it could be a bad or faulty time delay relay (if the unit is equipped), thermostat problem, transformer, safety control (low refrigerate) or wiring problem (broken or loose wires). The only way to make sure where the problem originates is to test using a volt meter. I would suggest turning off the power to your system and check all connections to make sure they are good and tight and not burnt. I would suggest turning the power back on and testing the controls with a volt meter to make sure 24 volts is coming out of every control. A good rule of thumb is: If the power is going into a control and not coming out then this is where the problem is… on the control where the power is not coming out. *Another note I would like to add for this problem would be that I know that many of the electric companies throughout the U.S. have installed energy conservation controls on many of the air conditioner and heat pump systems. If you have one of these controls on your AC or heat pump system (Please see pic below) then this allows your electric company to control when you unit operates. Under peak energy times your electric company can turn your system off. Also, I have found when I was doing service that once you turn the power off to the unit (pull the disconnect) this energy control will not allow the system to come back on for 8 to 10 minutes. This makes a service call very time consuming. When I was doing service, I would temporarily disconnect the energy control so I would not have to wait 10 minutes to test the system. If you have one of these energy controls then this could be the cause for your unit to not operate if your electric company has shut your unit down during peak energy times.

Above pic of energy control box on the right of the disconnect box.
Above pic of energy control box on the right of the disconnect box.

4. Customer Problem: Will a larger blower motor help my air conditioning? My air conditioner does not seem to be blowing very hard.

Answer: I would check your refrigerant charge first because if your system is low on charge it will cause the coil to freeze up and cause a restriction in the air flow. Rule of thumb is the blower should produce 440 CFM (cubic feet per minute) of air per ton. On a two ton system 880 cfm. This usually calculates out to be about a 1/4 to 1/3 HP blower motor. If you get too much cfm it is hard on the air conditioner, because it robs the air conditioner of the cool gas going back to the compressor to keep the compressor running cool. Most of the time if you increase the blower size beyond designed specifications, you have to over-charge the AC or heat pump unit to get the cool gas going back to the compressor so that it doesn’t burn the compressor up. I usually need to add refrigerant to a system that has too large of a blower motor. You want to charge your system so that there is cool gas going back to the compressor and the suction line feels like a cold coke can right out of the refrigerator. The air conditioner should make a 15 to 20 degree difference in the ambient air. If you home is 75 degrees inside the air coming out of the registers should be between 55 to 60. I hope I have answered your question. I have oversized blowers before to get more airflow. I would not recommend going over 1/3 horsepower in your case. You would need to check the charge after you install the new motor to make sure you are getting the needed cool gas back to the compressor. I would check to make sure your blower wheel (squirrel cage) is clean and the bottom of your evaporator coil is clean before trying a larger motor.

5. Customer Question: What are some tricks for removing a condensing unit fan blade?

Answer: When replacing a new condenser fan motor, sometimes the condenser fan blade is hard to get off! With the method I describe the scenario is that you have a bad condenser fan motor and you want to take the fan blade off so it can be used on a new replacement condenser fan motor. Most of the time the fan blade is easy to get off using the method that I describe below. I use this method all the time. Sand the existing shaft with sand cloth to remove the rust if any of the motor shaft is sticking up out of the hub. Use WD40 on shaft and lock nut. Loosen lock nut on blade. If the lock nut is stubborn and will not come loose, hit the top of the blade hub a few times lightly with a hammer to help the WD40 vibrate, penetrate into the threads. If the lock nut or allen screw will still not come loose then you might need to apply some heat with a torch. Cut the existing motor shaft off using an electric hack saw (Saws-All) or hack saw between the motor and the bottom of the fan blade. When finished cutting you should have the motor separated from the fan blade and shaft. It is tough going using a hand driven hack saw, but it can be done. Once you have the shaft cut off from the motor. Take the blade and lay it down on some concrete. Take a deep well socket 2″ to 3″ deep and position the socket underneath the hub on the fan blade and on the concrete. Take a hammer and drive the shaft out. When the shaft gets down below the top of the hub use a 3/8″ extension to drive to drive the shaft out of the hub. If you mushroom the top of the shaft you might need to drive the shaft back out from the other end a little bit and use a metal file to file away the mushroomed metal so the shaft can be driven out of the hub. Best of luck! This should work. This method has worked for me for many years!

6. Customer Problem: Why does my furnace air conditioner have poor air flow?

Answer: If your furnace or air conditioner has had a constant problem of poor air flow from the very beginning, then this could be caused by improperly designed duct work for your heating and air conditioning system. If you have just noticed this problem recently then this could be caused by a dirty filter, dirty blower wheel, stopped up evaporator coil, and a dragging motor can cause poor air flow. I would suggest turning off the power to you furnace or air handler and have your evaporator coil and blower wheel checked to make sure they are clean. Check the capacitor on the blower motor to make sure it is reading up to the specifications on the capacitor. If you do not have a capacitor tester then you would need to purchase a new capacitor to see if it is the capacitor. Make sure your system is fully charged with refrigerant. A system that is low on charge will cause a freeze up condition and block air flow through the evaporator coil. To identify which capacitor you need you would need to turn off your power and take the capacitor loose and try to read the specs on the capacitor. Here is a link to our page: Please click here to see a list of capacitors we sell. I hope that you can easily find the problem and fix it.

7. Customer Problem: What could be causing my indoor Air Conditioner, Heat pump coil to freeze up?

Answer: Indoor coil (evaporator coil) freeze ups are caused most of the time by a low refrigerant charge. Not enough refrigerant in the system. A dirty air filter can cause evaporator coil freeze ups. Before you call someone to check the charge on your system I would make sure the filter is clean. Freeze ups can also be caused by a dirty blower wheel, dragging motor (might need a new motor run capacitor) or a dirty evaporator coil ( might need to clean the under side of the coil). The most common cause most of the time is because the system is low on refrigerant charge. Once the evaporator is thawed out you can turn the air conditioner back on, but make sure the larger line is good and cold going back into the outdoor unit. You will need to possibly get under the black insulation and feel the bare copper line. After the unit runs for 10 to 15 minutes the line should feel like a cold coke can right out of the refrigerator. If it doesn’t then you are low on charge and need to get a technician to find the leak and charge it up as quick as possible. It is very hard on the compressor to run without enough refrigerate because a low on charge system will allow the compressor to over-heat, melt the compressor motor windings and burn the compressor up over time. When the compressor motor windings melt this contaminates and produces acid in the system. This is very bad on an AC system so please make sure your AC, Heat pump system is charged up properly.

8. Customer Problem: Why is water leaking on my floor with the air conditioner on? My service man says I need a new evaporator coil.

Answer: Most of the time when water leaks from an air conditioner on the floor the drain line is stopped up. I use compressed air, a Gallo Gun Drain line cleaner or a wet vac to try and unstop the drain line. Please click here if you are interested in the Gallo Gun drain line cleaner. Water leaking can also be caused by a leaking coil drain pan. The evaporator coil sets in a drain pan. If the pan rusts out and gets holes in it, it will leak. You or the service man would need to inspect the coil to see if the drain pan is leaking. This can be difficult and time consuming since the coil is usually cover up with sheet metal and you need to look under the coil bottom. This may be why your service man says you need a new coil. The coil drain pan is hard to repair and you usually have to take the coil completely out to repair the leak. Water on the floor can also be caused by a coil that freezes up or forms ice. This condition is usually caused by a low refrigerant charge, but can also be caused by a stopped up filter, dirty blower, dirty coil or a motor that is dragging (going bad) and not producing enough air flow. A weak capacitor could cause a motor to not run up to speed. I hope this helps you to find the problem.

9. Customer Problem: I pulled the high voltage disconnect on my outdoor unit. Why am I still getting a low humming sound?

Answer: The low humming sound is probably from the low voltage power still being on. The hum could probably be the contactor or reversing valve on a heat pump being energized. The low voltage power transformer is usually located on the indoor furnace or air handler. Sometimes the low voltage transformer is located on both the indoor unit and the outdoor unit. I would suggest turning the power off to the furnace or air handler. Usually there is a switch on the side of the furnace to do this. On an air handler there are usually breakers or a disconnect. The low voltage will not hurt you, but if you accidentally touch a low voltage wire and ground it out then you might damage your control board or blow a low voltage fuse on the board.

10. Customer Question: Is there an easy way to clean an evaporator coil?

Answer: There is not an easy way to clean an evaporator coil that I know of. When I was servicing furnaces (clean and check). I would always take the blower out of the furnace, clean the blower wheel and blower motor. While I had the blower out I would look up through the heat exchanger with a flash light to see if the evaporator really needed cleaning. This requires that you slide into the furnace blower compartment on your back and shine a flashlight up into the furnace so you can see and determine if the bottom of the evaporator is dirty or not. I did not want to go through the trouble of taking the sheet metal off from around the evaporator and find that it was not dirty and that I had wasted my time so while I have the blower out it was easy to inspect the bottom of the evaporator coil. If the evaporator coil was dirty and while the blower was out I would take the sheet metal off the front of the coil and I would use a spray coil cleaner, a fin comb and a vacuum cleaner to clean the coil. Cleaning the evaporator coil is quiet time consuming, but I was motivated by knowing that if the coil was dirty and stopped up, then the customer would notice a big difference in their heating and cooling air flow and they would notice a big difference in the heating and cooling bills. If your furnace is going off on high limit often then a dirty evaporator coil being stopped up with lint and dirt might be the problem.

11. Customer Problem: My AC on my RV will not start when using my generator. Will a compressor super boost help start my AC powered by a generator?

Answer: I have this question asked many times. I can not guarantee this will solve your problem, but I know a lot of people use them to help start an air conditioner when being powered by a generators. We have many people purchase the compressor hard start boosters to be used for this purpose. I would recommend the SPP6 located on the following page: Please click here to see the SPP6 compressor hard start booster

12. Customer Question: Please help me understand what this warning means on my AC: “Warning…never stop the cooling system by shutting off the main power. If the main power to your air conditioner is ever disconnected for more than three hours, turn off the thermostat. Then wait for at least three more hours after the power has been restored before turning the thermostat back on. Failure to follow this procedure could result in damage to your air conditioning system”

Answer: I know exactly what you are talking about on the warning not to turn your air conditioner on for 3 hours after the power has been off for more than 3 hours. This is a manufacturer’s warning and quiet honestly not many people abide or pay attention to it. The warning is there to prevent the compressor from possible valve damage that could occur if any liquid refrigerant has migrated, and is sitting inside the compressor. The compressor is made to pump a gas, not a liquid, and if any liquid refrigerant has migrated into the compressor during the power off period, then when the compressor is started back up the compressor could try to pump the liquid refrigerant and bend the valves, thus ruining the compressor. Many of the compressors have heaters in them, either external or internal that boil the liquid refrigerant off when power is restored. They recommend waiting three hours to make sure all the liquid refrigerant is boiled off. Most people do not abide by this, but if you want to make sure you do not damage your compressor it would be a good idea to wait the 3 hours.

13. Customer Problem: I ran our heat pump, air conditioner all night and it did great, but when I went outside this morning the unit was making this buzzing/humming sound. It still works correctly, but it makes that humming noise even when the unit is not running. In other words when the thermostat has the unit in the off mode it makes the noise, but when the temperature in the house rises and the thermostat turns the unit on everything is fine. (Does this make any sense?)

Answer: Many heat pumps have a reversing valve solenoid that is energized (24 volts AC) all the time in the cooling mode. This reversing valve solenoid is energized whether the unit is running or not. If the solenoid is getting old, or if the solenoid is out of alignment, or loose then the buzzing, humming sound will occur. Try to switch your thermostat to the heating mode and see if the hum is still present. If the hum is still present then you might have a noisy outdoor transformer. If the noise is so loud that it is bothersome then you may need to replace the reversing valve solenoid or transformer. Another thing I forgot to mention. You might want to test your transformer and make sure you are getting 24 to 28 volts AC out of the secondary on the transformer. If the transformer is producing low voltage (under 24 volts) then this would cause a loud humming, vibrating sound. Best of luck in finding the problem. Please make sure all the power is turned off before testing or inspecting your air conditioning parts. I would not want to see you or anyone get hurt or shocked.

14. Customer Question: I purchased a new programmable thermostat. My thermostat wiring only has only three wires. The thermostat instructions call for a red power wire, a yellow, green and white wire. My three wire colors are White, Yellow and Green. How do I wire this thermostat up?

Answer: Please always mark the wires with tape or labels as to which terminal they were connected to on the old thermostat before removing the thermostat wires from the old thermostat. I will be able to help you better. Do you have both heating and cooling? Most thermostats have a Red wire that is the power wire that usually connects to R & RC terminals of the thermostat, a Green wire that energizes the Fan relay (on the furnace or air handler), connected to the “G” terminal on the stat, a Yellow wire that energizes the outdoor unit’s contactor, if you have air conditioning using the “Y” terminal, and a white wire that energizes the gas valve or oil burner when you need heat connected to the “W” terminal. The thermostat acts as a switch, like a light switch. Red to white switch turns on the heat. Red to Green turns on the fan, Red to Yellow turns on the air conditioner. The main question would be do you have air conditioning? One of the wires almost has to be the hot wire. The color might not be red, but maybe they, the installer, used another color for the hot wire. You would need to look at your low voltage transformer, and trace the wire down that is coming out of the transformer to determine the color and which wire is the low voltage hot wire coming out of the low voltage transformer. Low voltage transformers will have a primary which is the 110 volt side and a secondary which is the low voltage 24 volt side. Both the primary and secondary have two wires. One wire is the hot wire and one wire is the ground, common or neutral. You would need to find out which wire is the hot wire on the secondary and attach this to the R on your thermostat.

15. Customer Problem: My 24 volt low voltage transformer continues to burn up. This is the second transformer. What could be the problem?

Answer: Yes, I have encountered this problem several times. This is most definitely a short to ground and you have to find out what or where the short is to solve the problem. Most of the time this problem ends up blowing the fuse on the board if you have one on your furnace’s control board, instead of the transformer. I usually suspect and have found that the thermostat wires are the problem, but other devices with coils and electronics can also cause this problem. I had a reversing valve coil cause this problem one time. Most of the time it is in the thermostat wiring. This is a pain and time consuming, but in order to find the problem I would turn off all the power to the unit, take all the low voltage thermostat wires loose from the thermostat, air handler, and outdoor unit. I would take a digital meter set to ohms and check between all the wires with the meter. You should not get a reading between any two wires if the wires are in good shape. If the wires are good you would need to test the components from each wire or terminal to ground. The meter should not move. This is a pain sometimes finding the problem. Many times I would find the problem where the wires were installed going through the furnace body. The thermostat wires would ground out on the furnace body. The vibration of the furnace or air handler over time had torn through the wire insulation and caused a short. Sometimes animals will chew through the wires and cause a short. Sometimes sun light on the wires over time will rot the insulation and short out the wires. I hope you can easily find the problem.

16. Customer Problem: I changed out my control board and my furnace blower motor continues to run constantly. Even if I disconnect the thermostat wires it continues to run the blower. The only way I can shut the blower off is to turn the power to the furnace off. What could be the problem?

Answer: Many furnaces (Bryant & Carrier) when first powered on will run the blower for a minute or two then shut off. This is a safety function of the furnace to eliminate any heat that is in the heat exchanger before the furnace begins its heating cycle. If your blower is running all the time… I would suggest that you test your limit control and roll-out switches to make sure they are not open. I have some pictures of limit controls and roll-out switches below. If a rollout switch or limit is open then the furnace thinks it has over-heated and the control board makes the blower run all the time. You would need to test these with a meter to make sure they are not open. Is your control board flashing a blink code? If it is blinking a fault code, try to read what the code says the problem is. The fault code key is usually located on the furnace door. I hope you can easily find and fix the problem.


17. Customer Problem: I installed the new capacitor and the compressor hard start booster I received. Now the outdoor fan will start briefly but the compressor does not. The power management box on the side of the house shuts off power in less than a second.

Answer: This sounds like you have a grounded out compressor since you say the breaker box is shutting down almost immediately when the air conditioner is turned on. I would suggest turning off your power to the unit and inspect to see if any of the wires inside the unit are burnt or grounding out. If you do not see any wires burnt or grounded out wires, then I would suggest that you remove the compressor terminal cover, then remove the 3 wires that go into the compressor. Test the three terminals on the compressor with an Ohm meter to see if the windings are grounded out. If they are grounded out you will need a new unit or compressor. To test the compressor to see if it is grounded out, you would set your meter to OHMs. You would touch one end of your test lead to a good ground like a copper pipe on your air conditioner. Then touch each of the three terminals on the compressor one at a time. This would be the compressor terminals (Start, Run & Common). You should not get any kind of reading (resistance) on your meter when testing these terminals. If you do get a resistance reading then the compressor is grounded out. Hope you find another problem and your compressor has not grounded out.

18. Customer Problem: I forgot how to wire up the dual round capacitor that I purchased from you. How do I go about wiring it up so it doesn’t blow the capacitor up again?

Answer: You would need to look at the wiring diagram that came with the unit. Usually the wiring diagram is glued to one of the panels on the air conditioner. Hope you can read it. Rule of thumb on wiring the capacitor is: Herm on capacitor goes to the start winding on the compressor, Fan on capacitor goes to brown fan wire that goes to the fan, and Com on the capacitor comes off one leg of the contactor to provide power to the capacitor. There are usually more than one wire connected to the Com terminal. The Com terminal is used so other components of the air conditioner can steal power off the Com connection.

19. Customer Problem: My air conditioning unit blows the circuit breaker after it runs for a while. What could be the problem? Would a super-boost compressor hard start booster help?

Answer: I would recommend that you check and see if the outside of your breaker is getting warm after the unit runs a while (20 minutes or more). If the breaker is warm on the outside, it could be arcing inside the breaker and causing the breaker to trip after a while. You might need a new breaker. This could also be a tight compressor and if this is the problem then, yes, the super boost could possibly help. It looks like you have a 4 ton unit so I would recommend the SPP6 or SPP8E. Please make sure your unit is charged up properly by feeling the larger copper pipe (suction line) while the unit is running. You will need to get your fingers on it underneath the insullation. The unit should have run for 15 minutes or more. The copper line should feel like a cold coke can right out of the refrigerator if the unit is charged proper. If it doesn’t feel real cold then you are probably low on charge. Being low on charge will burn a compressor up faster than anything. Do not purchase the super boost if you already have a hard start capacitor installed. Some units come with hard start boosters from the factory. If you are interested in an SPP6 compressor hard start booster then please click the following link: Please click here to see the SPP6 compressor hard start booster.

20. Customer Question: Why does a motor or compressor need a capacitor to run properly? What actually does a capacitor do?

Answer: Great question! The following explanation for what the purpose of a run capacitor is came from my HVAC teacher when I went to HVAC school. I know there are more complex explanations, but this is the easiest to understand. On alternating current (AC) the current alternates on the voltage from zero to 110 or from zero to 220 volts 60 cycles per second. The run capacitor throws a stored charge in when the voltage reaches the zero point and keeps the voltage steady instead of all the up and down voltage drops. This makes the motor or compressor run smoothly and more efficient. This is easily seen on an oscilloscope where you can see the AC current going up and down. 60 cycles per second is pretty durn fast! It is amazing! If a run capacitor is bad or weak most of the time a motor will run slow or not run at all. I have heard furnace blower motors just sit and hum trying to start when the capacitor is weak or bad. I have also seen motors run real slow when a capacitor is weak. Capacitor life span and capacitor problems are common. I would suggest having an extra motor run capacitor and air conditioner run capacitor on hand so you are not stuck on a cold winters night or a hot summer day without one. We sell capacitors on the following page: Please click here to see the capacitors we sell.

21. Customer Problem: I own several rental properties. I am having a problem with moisture buildup in my pressure tubes on my 80% furnaces. The tubes stop up with water and the furnaces shut down. Below I explain how I eliminated this pressure switch problem.

Pressure Switch Problem Resolved: I’m responding to this very old email response from you. FYI, regarding moisture buildup in pressure tubes, I simply moved the pressure switch above where the tube connects to the inducer and the moisture problem went away (on both Goodman & Rheem furnaces). Thought you’d be interested. I’m from Portland OR where the humidity is fairly high in the winter…

22. Customer Problem: How to repair a 3 wire pilot burner on a Bryant Carrier furnace?

Bryant Carrier 3 Wire Pilot Burner Problem Resolved: This customer was kind enough to share with me how he repaired his Bryant Carrier 3 Wire pilot burner. This customer had installed a new 3 wire pilot burner, then decided to clean the old 3 wire pilot burner to see if he could get it working. Sure enough he got it working again after 20 years of service!

FYI – Without making any adjustments to the Gas Flow, I noticed on the new 3 wire pilot burner, that less of the pilot flame appeared to be striking the heat sensing switch plate when the blower kicked in. So I re-installed it after performing the below maintenance and it too worked again. However, I figured 20 years of service was good enough and retired the old 3 wire pilot with the new one. Below are the maintenance that I performed on the old 3 wire pilot and got it working again.

a) From inside the chamber where the gas would enter the Pilot Burner and the brass fitting screws in, I blew out the Gas Nozzle and the little cone nipple that the compression fitting sits into. The hole on the cone looked a little stopped up.

b) Took Sand Paper to the strike plate and wet sanded it back to bare metal again.
It looked like the blower kicking in was stealing enough of the pilot flame away from the strike heat sensing plate to cause it to cut in and out. After cleaning the pilot and furnace worked right again.

23. Customer Problem: I purchased a flame sensor from you hoping this would solve my furnace lock-out problem. My furnace still locks out occasionally. I have to reset the power switch before it will start up again.

Answer: I am sorry to hear that you are still having furnace problems. I try to help people out by giving them the easiest and least expensive solutions to their problems that I have seen over the years in our HVAC business. Sometimes other components, parts can cause problems. Sounds like you have an occasional problem that is going to be hard to find because it only does it sometime. You almost have to be there when the problem occurs with a meter to test and find out what the problem is. Many times the furnace control board will give you a flash code telling what the problem might be. I would suggest if your furnace is equipped with a control board that has a flash code that you read the code the next time the problem occurs. This problem could be caused by a safety control problem (pressure switch, limit switch) a loose or bad wire connection, or a control board problem. Please make sure all your wire connections and plugs are good and tight. Please make sure you have a good ground on the furnace.

24. Customer Question: My outside AC unit is humming but no fan or compressor action. Sounds like I have a capacitor problem. I’d like to buy replacement capacitors but they are round. Can I use oval caps with the same rating? Can I leave them loose since the brackets are for round caps?

Answer: Since your fan and compressor are not running I would like to suggest that you test the line voltage with a volt meter to see if you have 220 to 245 volts on L1 and L2 of your contactor. Please be careful when working with high voltage electricity. I would not want to see or hear of anyone getting hurt. Another question is: Are the contacts on your contactor closing when your air conditioner is calling for cooling? You should be getting 24 to 28 volts to your contactor’s coil when your thermostat is calling for cooling. If the contacts on your contactor are not closing then you might have a contactor problem or an AC safety control problem (high or low pressure safety control). If your refrigerant charge is low on some units the low pressure safety control will not allow the unit to come on until the refrigerant charge is at the right level. If your contactor is closing and you are getting voltage 220 to 245 volts through the contactor then this could be like you say a capacitor problem. If you understand the electrical wiring it would be the easiest to purchase a dual 40/5 MFD 440 volt dual capacitor. The exact replacement capacitor for what you now have. There are three connections on a dual capacitor. Com, Herm, & Fan. Common (COM) on the capacitor would come from your power source usually from the contactor. Herm connection would go to the start winding on your compressor, Fan would go to the fan, usually a brown wire. It is not recommended to replace a 40 MFD capacitor with a 45 MFD capacitor. Here is a link to our site if you want to purchase a capacitor: Please click here to see the capacitors we sell. You would need to secure the capacitors so the wire terminals do not touch anything metal or each other. I usually tape the connections on top of the capacitor with electrical tape and secure the capacitors to the frame with plumber’s pipe strap. Please make sure you do not drill through your condenser coil when drilling the holes for the pipe strap.

25. Customer Question: I remember reading somewhere on your site about lights dimming on A/C start-up. My lights are starting to dim more this year and last vs. when I put in my Bryant unit about 5 years ago. Is this the starter capacitor, you think? Where on your sight do you sell the replacements if this would be the main culprit? Thanks in advance.

Answer: Lights dimming on air conditioner start up can be caused by several things:

1: Circuit breaker going bad. See if you breaker is getting warm by touching the outside of the breaker after your air conditioner has run for a while. If the breaker is warm then you have arcing inside the breaker and need a new breaker.

2. Loose wiring. After turning off the power and checking to make sure the power is off with a volt meter. Make sure all wire connections are good and tight from the breaker through the air conditioners contactor to the Compressor terminal wires. If you still have a lights dimming problem I would suggest calling in an electrician to check and make sure you do not have any loose connections on your electrical meter or breaker box. The three main wires that come off the electrical pole can become loose, cause arcing, heat and cause your lights in your home to dim. Loose wire connections cause high amperage and can cause lights to dim.

3. Capacitors going bad or getting weak. Test capacitors with a capacitor tester. We sell capacitors on the following page: Please click here to see the capacitors we sell.

4. Compressor getting tight. Compressors that are worn can become tight and hard to start. A compressor hard start booster might help this situation. We sell compressor hard start boosters on the following page: Please click here to see compressor hard start boosters.

5. Low voltage from your house. You should be getting at least 220 to 245 volts to your air conditioner. Call your electric company supplier or a licensed electrician if you voltage is low. I have tried to cover a few of the things that can cause lights to dim when your air conditioner comes on.

26. Customer Problem: My outdoor air conditioning unit’s high pressure switch trips ever so often. Why does it high pressure switch trip so often?

Answer: The high pressure switch that trips often can be caused by several things:

1. Dirty outdoor coil. Turn off power to your AC or heat pump unit and clean the coil with a garden hose.

2. Slow or dragging fan motor. Replace motor or capacitor. I would need to know the capacitor specs to recommend a replacement capacitor. I would need to know the unit’s model number in order to recommend a new condenser fan motor. Please email us at anytime: support@arnoldservice.com

3. Motor or fan blade going the wrong direction. Air should come out of the top of your unit.

4. System over-charged with refrigerant.

5. Faulty high pressure switch tripping without having high pressure. High pressure switches are usually set to trip at a little over 300 psi. Sometimes I have seen switches trip for no reason at all.

6. Extreme high outdoor temperatures above 100 degrees. Your outdoor unit has to be clean to run properly under high outdoor temperatures. Please make sure your unit’s coil is good and clean.

27. Customer Problem: I recently purchased a pressure switch for my Carrier furnace, HK06NB124. According to all the material and research this was the correct one for my furnace, but I continue to get the same pressure switch code problem. Is the pressure switch faulty or do I have another problem?

Answer: From my experience over the years most of the time the pressure switch is not the problem. I have found that the draft inducer, hole going into the draft inducer can become partially or completely stopped up. The flue vent of the furnace can become obstructed or partially stopped up. Since your furnace is a high efficiency condensing furnace and has a drain the drain could be partially stopped up. If the drain is not draining properly this will cause the pressure switch to shut the furnace down. If any of the drain hoses have holes in them or are stopped up this will cause the pressure switch to shut the furnace down. Improper venting (too many turns and distance) can cause pressure switch problems. Debris (junk) obstructions inside the vent can cause problems. Last but not least if the draft inducer is tight (bearings dragging or going bad) and not producing enough draft then this can be the problem. A draft inducer that has a weak capacitor (if equipped) can run slow and cause the pressure switch to not work properly. Please click here if you would like to see our: How to test and troubleshoot gas furnace pressure switches page. I hope you can easily find the problem.

28. Customer Problem: I purchased a flame sensor from you for my Goodman furnace. The new flame sensor did not fix the problem. My furnace still lights for 7 to 10 seconds and then the gas goes out. What could be the problem?

Answer: Since your furnace is still having what sounds like flame sensing problems I would suggest making sure the flame sensor is positioned in the flame where it is getting a good blue flame to sense. I would suggest checking all connections to make sure they are tight (especially the ground connection on the transformer). Check your plug in connection that goes between the blower section and burner section of your furnace to make sure it is good and tight. Check wire and flame sensor connections to make sure they are tight. I would recommend checking all rollout switches, limit switch and pressure switch to make sure they are staying closed (current flowing through) them all the time. This could be a control board problem again, not sensing the flame. We have some troubleshooting tips on the following page: Click here: Troubleshooting Heating Problems I hope you can easily find the problem.

29. Customer’s Problem: I have a question, I am working on my mothers heater, a few days ago the heater would come on and shut off and then the heat would not come back on a second time. The first time I checked it the thermostat called for heat, inducer came on but no ignitor glow so I took two wires going to what I believe its a high limit thermostat switch coming from the board and jumped them and heard a click by the gas valve and the ignitor came on and then it worked came on and shut off a few times then it stopped. When heater is off for a while and I turn it on with the thermostat call for heat, the inducer comes on, ignitor glows but no heat. so I jumped those same wires again and now the ignitor doesn’t glow it will glow only after heater has been off for a while what could be the problem? any suggestions would help thank you. the unit is a package Goodman model # pg8060100-1.

Answer: I am not familiar with this Goodman furnace model so I’m probably not going to be much help. I would suggest that when you are having problems to get a volt meter, set it to “Volts AC” and test each of your safety controls (pressure switch, rollout switches and limit switch) to see if they are all closed. With the furnace calling for heat you can touch with your meter probe from each terminal to ground and see it they are all getting 24 to 28 volts through the controls. So you would take the meter and touch one probe on the terminal (of the control) and the other probe to a ground (body of furnace). If it isn’t getting 24 volts through each of the terminals then either the control is bad, your heater is over-heating, or you have a cracked heat exchanger (if it is a rollout or limit). If it is a pressure switch then either the pressure switch is bad or your vent or drain is stopped up (if you have a condensing furnace). Also make sure you check all your wiring to make sure all wires and connections are tight. Especially pay close attention to the ground wire coming off the transformer.

30. Customer Problem: I have a Carrier A/C condenser unit model 38CKB036. The fan on the unit recently started running continuously, and runs at about 400-500 RPM vs. the rated 1500 RPM. The only way I can stop it is to cut the power at the disconnect. I have replaced the dual run capacitor with no effect and have removed and cleaned / check the contactor. Any idea what can cause this? I am a bit surprised that there is power to the fan when the contacts are open.

Answer: This problem can be caused by a short to ground in the motor or a short to ground in the motor wires that lead to the motor. With a single pole contactor there is 110 volts always applied to one lead on the motor at all times, and even if the contactor is not energized it can supply 110 to the motor. If the motor or wires are grounded out then it will run half speed. I would suggest turning off the power (of course), take the black and yellow wires loose from there connections. Use an ohm meter and check from the black to ground and yellow to ground. If you get any resistance then the motor is grounded out and you will need a new motor or repair the wires on the motor. I hope you can find the problem easily.

31. Customer Problem: Outdoor air conditioning unit is running but the indoor furnace blower will not run with the fan in the “Auto” position on the thermostat and the thermostat calling for cooling. What do you think the problem is?

Answer: This could either be the thermostat, capacitor, blower motor or control board that is causing the fan on your furnace to not come on. I would start by checking the thermostat. Check with a volt meter between the G (green) and C (com) terminals with the fan in the auto position and the unit calling for cooling. (You might have to tape the blower door safety switch closed to do the testing) Please be careful to not get shocked. You should get 24 to 28 volts between the G & C terminals. If you do not then you either have a thermostat problem or a wiring problem. If the G & C check out OK then go to the terminals that provide power to the blower motor and see if you are getting 110 to 125 volts to the blower motor. If you are the control board is OK and probably the blower motor is bad or the capacitor is weak or bad. I would suggest taking the capacitor to an appliance parts place and see if they will test it for you. I hope you can easily find and fix the problem.

32. Customer Problem: My furnace wobbles and shakes sometimes. What could be the problem?

Answer: Most of the time wobbling inside the furnace is caused by the blower wheel being out of balance. Most of the time a piece of something (filter, paper, furnace insulation, dirt) is sucked into the blower wheel (squirrel cage) and causes it to become off balance and wobble. I would recommend turning off the power to the furnace, taking the blower door off and inspecting the blower wheel with a flash light and a mirror. Sometimes the blower wheel balance weights can fall off and this will also cause so blower wheel wobble. Many times it is hard finding the weights and where they should be place if they have fallen off. It is almost better to replace the whole blower wheel if the weights have fallen off. The weights usually only one or two are little pieces of U shaped metal that friction fit on to the blower wheel fins. A motor with the bearings going out can also cause wobble, but most of the time it is the blower wheel out of balance that causes wobble.

33. Customer Problem: Propane furnace not working when temperature got down below freezing.

Customer Found the Answer and wanted to help others by letting others know about this problem! Fantastic!: Mr. Misner wrote the following: Had this problem for 6 years. Two heating companies and Propane company could not figure the problem out. Mr. Misner writes:“The problem was that my propane furnace would quit working and by the time the service man arrived it was working again and since no one could find the problem I depended on my fireplace insert for most of my heat. I live in Southwest Missouri and for the most part our winters are fairly mild. With temps during the day normally above freezing and dropping below at night. Then this last time I was checking the furnace. I noticed that there was no LPG odor so I went online and came across this web-site: www.propane101.com . This problem was not only overlooked by a house inspector when I purchased my house but by two furnace repair men and two different propane companies. I bought a used propane tank last year and the propane company who installed it missed this. I had a two stage LPG regulator system (one regulator on the tank and the other one on my outside furnace). The second stage regulator was not installed properly. It was installed horizontally with the vent facing slightly up (on the regulator it says if installed with no cover the vent is to face down). When it would get below freezing the moisture in the regulator would freeze the regulator shut and not allow propane through. I understand that it can also freeze open. I thank God that the regulator did not freeze open (cause and explosion) and I thank you for listening to God’s calling. I hope you will add the web-site: www.propane101.com to your web-page and inform people of the proper installations of regulators. By the way my tank is 35 feet from my house and my furnace is the only thing that uses propane so I changed to the integral twin stage system and last night it was just below freezing and it worked. THANK YOU!” Thank you so very much Mr. Misner! The information that you provided is very valuable for the safety of other people that use propane gas!

34. Customer Problem: Gas on furnace is shutting off after 3 minutes of burn time.

Answer: You would need to test some controls to see what the problem is. Why is the gas shutting off after 3 minutes of burn time. I have some troubleshooting tips on the following page: Click here: Troubleshooting Heating Problems I would start with testing the thermostat to make sure it is getting a constant 24 to 28 volts between the W and C (com) wires when calling for heat. If the thermostat isn’t getting 24 volts after the 3 minutes then you might try adjusting the anticipator if equipped. The new digital thermostats do not have an anticipator setting but have batteries. Please make sure the batteries in the thermostat are in good shape. I would suggest testing all the safety controls, ie limit, pressure switch, rollout switches to make sure they are all staying closed. Test the controls to make sure they are staying closed when the furnace shuts off after the 3 minutes. This sounds like the furnace might be overheating (going off on limit) and shutting down. This overheating could be caused by a dirty filter, dirty blower wheel, slow blower motor (could be a weak capacitor) gas pressure set to high on the gas valve, improper setting on the thermostat anticipator (if equipped), over-sized furnace (too big for your home or duct work) or a stopped up evaporator coil.

35. Customer Problem: York Control board problem-Blinking 9 blinks after installation and not working- Reverse Polarity Problem.

Answer from one of our customer’s Garry: Just wanted to follow-up…figured out the problem described in my email…the following may help with future customers who buy this board. As you know, I bought the S1-33102956000 which has been updated to the S1-33103010000 control board for my York P2MP furnace. I installed it and the furnace would not work. Upon installation, I got the recurring nine blinking lights error code which means reverse polarity problem or control board not grounded. Here’s what I found out. Apparently, the polarity of the new, upgraded control board is reverse (in polarity) in design from the OEM control board. To get the furnace to work with the new control board simply reverse two wires when connecting them to the new control board. There are two 24V wires that come from the transformer to the control board. A light brown wire connects to the lead labeled “XFMR” (near the black, blue and red wires and leads)… the other white wire coming from the transformer connects to a neutral lead. Reverse these two wires…put the white on the XFMR lead and the light brown wire on the neutral lead….and then the furnace will work. Hope this helps….I like your web site – it has a lot of useful, helpful information; and I plan to order some more parts from you in the future…I think I am going to replace parts before they break…novel idea! Take care, Garry

36. Customer’s Problem: Hello, I am troubleshooting my hvac problem and am wondering whether the compressor super boost product may work for me? How do I know if the compressor is broken or simply stuck? As soon as I turn the unit on the fan runs, and perhaps the compressor but I cannot tell, for about 10 seconds then the breaker trips. I have replaced the capacitor already and it did not solve the problem. My contacts were dirty and I have cleaned them. Same problem appears. I am praying that I do not have to replace the compressor…Any thoughts on this would be greatly appreciated.

Answer: Sorry to report, but most of the time when the compressor is tripping the breaker on start up it is caused by the compressor grounding out and you would need a new compressor. The only way to tell for sure if the compressor is stuck or grounding out causing the breaker to trip is with an amprobe type meter and an ohm meter. Please see the picture of the meter below. We sell this meter on the following page: Click here: Heating and Air Conditioning Parts and Supplies The amprobe meter has jaws that open and wrap around one of your compressor wires. When you turn the power on to start your AC and if the meters jumps up to over 60 amps and holds until the breaker trips then it is a stuck compressor. Normal startup would be the amps would jump to around 60 or above for a split second then go back down to a normal RLA (running load amps) is probably between 10 and 20 amps depending on the size of your unit. RLA should be listed on the label of your air conditioning unit. If you want to see if the compressor is grounding out you would need to turn the power off to the unit. Take of the compressor terminal cover, remove the three wires from the terminals, set your ohm meter to ohms and test from each terminal to ground (copper pipe on your unit). You meter should not show any resistance between each terminal to ground. If it does show resistance your compressor is grounding out and you need a new compressor or new unit. If the compressor is stuck or locked sometimes the SPP6 can unlock it. I have seen the SPP6 compressor hard start booster save many a compressor from the junk yard We sell the SPP6 on the following page: Click here: Compressor Hard Start Boosters I hope you do not need a new compressor. Steve

37. Customer Problem: The 3 amp fuse on my control board keeps blowing. What could be the problem?

Answer: This could be a control board problem, but most of the time this problem is caused by the thermostat wires shorting out somewhere. I would suggest looking to see if you can see where the wires might be shorting out. During the air conditioning season most of the time the wires short out near the outdoor unit where the thermostat wires are exposed to the weather and animals. Many times animals will bite through the wires. If you want to look for shorts indoors then the wires are most of the time shorted where they come through the frame of the furnace or where they are wrapped around a nail. If you cannot find any visual signs of where the wires are shorted then I would suggest that you turn the power off to the furnace take all thermostat wires loose from the control board taking note of where the wires go back. Take a jumper wire and jump between the R and W terminals on the board. This should jump past the thermostat and thermostat wires. Turn the furnace power back on. The heat should work when the power is applied. If it blows the fuse again then you have a control board problem or a low voltage problem within the furnace controls. If the furnace works then you have a thermostat wire problem or a shorted thermostat problem. Most of the time the thermostat wires have to be replaced if you cannot visually find the short. I hope that you find the problem easily.

38. Customer Question: I have a new 45k 95% goodman furnace. I would like to know what is common and likely to go wrong – and perhaps purchase those items likely to go out ahead of time so that when it does go out, I have the part on hand and can replace it. Is there a good way of doing this?

Answer: Thanks so much for your interest in our website! I have a 94% Bryant furnace and I like to keep an ignitor, flame sensor, control board and draft inducer on hand. The blower motor is over $400 so I do not keep one of these. On our furnace the control board and draft inducer are real expensive over $250 each. Most Goodman furnace parts are warranted for at least 5 years and your furnace since it is a 95% furnace might be 10 years. The heat exchanger probably has a life time warranty. If it were me I would suggest keeping an ignitor and flame sensor the least expensive parts. If you want me to look up parts please send your furnace’s model number and I will give you a parts list. The model number should be located inside the furnace near the burners. Most of the 95% furnaces are pretty complex so you might want to call a tech if something goes wrong. I would recommend looking at the flame sensor and ignitor and see how difficult it would be to replace it before ordering. Please send me the furnace model number at our email address: support@arnoldservice.com

Please Remember Safety First

Please read our disclaimer and safety related information below before attempting to do any type of Heating or Air Conditioning Repair. We do not want to see anyone get hurt or shocked!

Thank You!

*Please always turn off all electrical power, and discharge the capacitor/capacitors (if working around capacitors) before attempting to inspect or repair any heating & air conditioning equipment. Check to make sure the electrical power is off with a reliable meter. I have never been shocked by a capacitor (knock on wood) and rarely see them discharge, but it is a good idea to discharge them before working around them. Please read below. It tells you how to discharge a capacitor.

How To Discharge The High Voltage Capacitor:

The capacitor is discharged by creating a short circuit (direct connection) between the two capacitor terminals and from each terminal to chassis ground (bare metal surface). Please make sure that you are touching the insulated screw driver handle and not the metal part of the screw driver before attempting this procedure.

  1. Do this by touching the blade of an insulated-handled screw driver to one terminal, then slide it toward the other terminal until it makes contact and hold it there for a few seconds. (Sometimes this can result in a rather “pop!”)
  2. Repeat the procedure to create a short between each capacitor terminal and chassis ground.
  3. If the capacitor has three terminals, use the same procedure to create a short circuit between each terminal and then from each terminal to ground.

Disclaimer: Arnold’s Service Company, Inc. assumes no liability for any incidental, consequential or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user. Although careful precaution has been taken in the preparation of this website information, we assume no responsibility for omissions or errors.

140 thoughts on “Popular HVAC Questions & Answers

  1. My daughter just called to tell me that after she turned on the furnace she smelled something coming from the vents. She described it as either a propane smell or gas. Our local gas supplier came out and told us that the left 2 burners, the 2 furthest from the glow bar are not staying on after ignition flames coming out of burner chamber. Are you able to tell me what this might be?

    1. Hi! This can be a dangerous condition because when all the burners do not light it can cause raw gas to go up into the heat ex-changer and cause lots of black soot to form and stop up the heat ex-changer so the furnace does not vent properly. I would suggest that you call an HVAC company and have them clean and inspect your furnace. I hope you get this fixed soon. Steve

  2. Also, is it possible that the capacitor has been deteriorating and finally just blew? (pardon my ignorance).

    1. Yes, the capacitor could be weak. I would suggest having the capacitor tested to make sure it is in good condition.

  3. Hi–
    I have a riello 50 f5 burner. It hasn’t been firing up. I find that if I take the control box off, jump connections 5-6 and manually get the motor started, then I can have a hot shower and some heat in the house. I’m just trying to get by until I have a gas line installed in a couple of months.
    Today while putting on the jumper cable I accidentally touched something ( I don’t know what) and there was a spark, something shorted out and there now seems to be no power going to the motor. The control box was off, so that is ok. The circuit breakers are all ok.
    Is there a fuse tripped somewhere? Did I fry the motor? Help!

    1. I am sorry, but I do not know anything about the Riello 50 f5 you are have installed. I would suggest looking for a low voltage fuse on the circuit board. Hope it burned out the fuse and not the electronics. Sorry that I can not give you any advice. Steve

  4. My outside compressor fan gets hung up every once in awhile after being away from my home for a few weeks. After freeing the fan, everything works fine. Any suggestions on what to have check or some issue suggestions as I do not want to be away for months with the AC not running to keep humidity levels respectable.

    1. Hi Robert! Thanks for asking this question. Since you say, “After freeing the fan” I expect that you have a tight bearing in your fan motor and if your fan motor does not have oil ports (most do not) I would suggest replacing the fan motor because a worn or tight motor bearing will be a constant problem. It is very hard on the compressor to run without a fan motor. This can cause the compressor to run high head pressure, over-heat and turn off and on while you are away on thermal over-load. The compressor thermal over-load has just so many resets and then you will need a new compressor or a new unit. If the fan blade is free to turn then I would suggest that you have the capacitor tested to make sure it is in good shape. Weak capacitors are a leading cause of fan motor and compressor failure. You should be able to spin the fan blade and the blade should continue to spin for a few seconds. If it doesn’t then you have a tight motor bearing and need to replace the motor. Send me your unit’s model number if you would like for me to look up your unit’s motor part number. I will try to make a recommendation if you think the motor bearings are going out. I hope you can get this fixed. Steve

      1. Thank you very kindly for your timely response which is very rare no a days.
        The AC is a Lennox 5kw Elite Serier CB30M Air Handler with model number CB30M-21/26-4P

      2. Hi Robert! Thank you so very much for your kind words! I am sorry, but I do not have a Lennox parts program where I can look up parts. I can not find a Lennox parts supplier here in Louisville, KY. where I can call for information and purchase parts. Here is a link to a place where you might be able to find parts for your air handler: https://www.repairclinic.com/Shop-For-Parts/a39b367d1234262/Model-CB30M511P-Lennox-Air-Handler-Parts Sorry that I can not help you out more! Hope you have a great day! Steve

  5. i installed a new revolv hvac system about 6 years ago and the blower has always been loud.do you think the fan blades are wrong.the old unit was not as loud as the new unit is.

    1. I am sorry, I do not know anything about a “revolv” hvac system. I have never heard of this name brand. Loud blower noises can be caused by several things: (1) Blower wheel off balance and vibrates (2) loose blower motor bears which cause blower wheel vibration and wobble (3) too large of a blower or too much air flow for the duct work. If the installer installed a blower that is too large for the duct work that you have then this will be noisy. The air flow through the duct work will be noisy if the duct work is too small. You might try a lower blower speed if possible. (4) A foreign object could be stuck in the blower wheel causing it to be off-balance. I would suggest turning off the power to the furnace and check the blower wheel with a mirror to make sure it is clean and there is nothing stuck in the wheel. I hope you can find an easy solution to the noise problem. Steve

  6. Hi Steve, so my transformer is working correctly, I get 24 volts to the thermostat and also get 24 volts coming outside when I check the wires with my volt meter. Those wires then tie into the defrost control board. But, I’m not getting 24 volts coming out of the board which is not providing 24 volts to the contractor. When I turn my thermostat to cool mode it clicks on and then immediately it blows my 5 amp fuse on the furnace and everything shuts down. Now if I go outside to the outside unit and pull the breaker out to cut off all power to the outside unit and then turn the thermostat back on to cool setting after replacing 5 amp fuse, the furnace stays on and doesn’t blow the fuse. So why does the furnace run with no power to the outside unit but the furnace blows the fuse when there is power turned on to the outside unit? Do I have a bad defrost control board? Thank you for any help!

    1. Hi Mr. Thorn! Blowing a fuse on the control board shows that there is a short to ground somewhere in the system. Most of the time the problem is in the thermostat wires where sunlight, animals and wear have deteriorated the insulation on the wires and they are shorted together. I would suggest that you inspect the thermostat wires. Sometimes inspection does not show the short and you would need to take the wires loose from both ends and test with an Ohm meter. You should not have any resistance between any two wire once they have been disconnected. Sometimes it is easier just to replace the thermostat wires. If this does not fix the problem then you could have a short to ground in the defrost board, reversing valve coil or contactor. I would try directly connecting the yellow wire to the contactor (by-passing the defrost board) and see if it still blows the fuse. If it doesn’t blow the fuse then the problem is in the defrost board. I hope you can easily find and fix the problem. Steve

  7. I had some siding replaced near my ac unit, and when they removed the disconnect, they shorted out the breaker. I replaced with new pull out disconnect, have voltage to unit, can push in the contactor, and manually start the compressor, but had no 24 volts to the board. so I thought they may have blown the board. this Goodman unit is 2 years old… So I checked the thermostat, no 24 volts to the outside. replaced the transformer.
    just for good measure, replaced the outside contactor. everything is now NEW..
    still no low voltage to outside… noticed that one of the wires on the double stack sequencer was a little dark, the thermostat still is working, fan cycles on heat, cool, and emergency, elements are heating, just still no compressor, or heat pump..
    could a sequencer be my problem??

    1. Hi Richard! Sorry to hear that you are having so much trouble with your heat pump after the siding installation. I would make sure that your thermostat wires that go out to the unit are in good shape and not broken or shorted out. On most heat pumps the yellow wire “Y” that closes (provides power) the outdoor heat pump contactor is connected directly from the thermostat to the outdoor contactor. Many times they will connect the yellow wire with a wire nut inside the air handler. I would suggest that you test between the yellow wire and C (com) with a meter set to “volts AC” with the thermostat calling for heating or cooling. You should have 24 to 28 volts AC between the two wires. If you do not then you either have a broken wire or a thermostat problem. I hope you can easily find and fix the problem. Steve

      1. Like I stated, wires are all good no cuts, no breaks.
        the transformer wire goes to the m1-m4 sequencer, no voltage out to the contactor.
        can I jump the sequencer to test it,?
        does it even pass 24 volts to the contactor,??
        or is it just to energize the upper stack on the sequencer to supply power to the heating elements?
        simply, my question is, if your sequencer is stuck, so that you are still getting voltage to the heat elements,…..
        and the lower 24 volt plate is defective,…..
        will it not pass voltage (24) to supply the contactor?
        or does the sequencer not have anything to do with it at all?

      2. Hi! I am sorry, I do not know what the problem with your heat pump is. You or I would have to study the unit’s wiring skematic to get an idea of what the sequencers purposes are in your system. In all the heat pumps that I worked on over the years the sequencer should not have anything to do with the outdoor unit’s contactor being energized unless one of them has shorted out and caused the whole low voltage system to be disrupted. Most of the time the sequencers are used to energize heating elements and to start the blower motor, but not connected to the contactor in anyway. That is what the “Y” connection on your thermostat should be used for to energize the contactor and it should be a direct wire (usually yellow) which goes to the contactor coil. I am sorry that I do not know the answer to your questions. I hope that maybe someone who reads this might have an answer. Sorry
        to disappoint you. Steve

  8. Hello – I am trying to install a Smart Thermostat and not getting 24v on the C wire. Here is my current wiring from the old setup. On the HVAC side (Control Board and Transformer, it has the following wires connecting to the wire going into the house:

    C Blue
    O White
    R Red
    Y Yellow

    *There is a G wire, however it is not hooked up to anything on the outside unit and the control board has no G terminal.

    On the Thermostat side I have the following:
    C Blue
    O White
    Rh Red
    Rc Jumpered to Rh
    Y1 Yellow
    G Green
    W1 Jumpered to Y1

    When I test the R wire to the C wire, I get nothing on the volt meter. I will get 27volts when testing the following with the probes: R and G, R and O, R and Y.

    Unit is a Goodman with AC / HP. Air Handler is in the attic.


    1. Hi! I am sorry, but I am afraid to advise you on this. I do not understand why you only have 4 wires on your old thermostat and why the G wire is not hooked up. On a heat pump you should have at least 6 wires coming to the thermostat with these colors and functions being the rule of thumb: (1) R (red) hot wire coming from the hot side of the low voltage transformer. (2) C (com) common wire usually blue in color coming off the common side of the low voltage transformer. (3) Y (yellow) wire going to the contactor of the outdoor heat pump unit. (4) G (green) going to the fan relay on the indoor air handler (5) W (white) going to the first stage electric heat or auxiliary heat. (6) O (orange) goes to the reversing valve on the out door unit. Most heat pumps energize the reversing valve in the cooling mode. I am sorry that I can not help you out. Sorry to say, but you might need to trace each wire down and see where the wire is attached in the air handler and outdoor unit. Sorry, this can be time consuming. I hope you have a nice day and weekend!

  9. Hi, I just got what I was told was the replacement part (Honeywell VR8215S1289) for my Honeywell gas valve (VR8205M 2443). They look identical except that my current gas valve has a flex tube leading to the pressure switch. There is a hole next to the vent screw that an adapter screws into and the flex tube fits into the adapter, the other end goes into the pressure switch. There is no hole next to the vent screw on the replacement and I couldn’t find any hole to screw the adapter into for the flex hose. Could I go ahead and use the gas valve without the flex hose or should I scrounge the internet for my original gas valve?

    1. Hi Ade! I am sorry, but I do not know the specifications on the gas valve you purchased. I would suggest that you call or contact Honeywell customer support to see if they can help you out. Sorry that I can not help. Steve

      1. Thanks for your response. I went ahead and used the gas valve and it seems to work fine as I can hear the puff of gas before the blower kicks in. The problem now is that the burners are not glowing before the gas kicks in and the blower engages, so I get no heat. I tested the igniter and the resistance showed at 90 which is between the required range of between 50 and 400. Could the igniter be showing within range and still be problematic. Is 90 not good enough. It’s a Nordyne 903758 and it’s gotta be about 15 years old. Unless I am wrong I would also think my furnace would shut down of there is no flame but it continues blowing cold air. Help.

      2. Hi Ade! I tested one of the new 903758 ignitors that I have and it read 71 ohms. I would think that 90 would mean a good ignitor. I would suggest testing to see if you are getting 110 volts to the ignitor from the control board when the ignitor should be glowing. Please make sure all the safety controls are closed like the pressure switch and limit. Also make sure the rollout switch are all closed. If these are all closed and you are not getting 110 volts to the ignitor then you might have a control board problem. I hope you can easily find and fix the problem. Steve

      3. Thanks Arnold. I just replaced the motherboard. I think I’m going to call in a professional at this point for some diagnosis. I don’t like to monkey around with electricity. Thanks again.

      4. You are welcome! I hope the tech can easily find and fix the problem with your furnace. Hope you have a great day! Steve

  10. i am trying to run a seperate line to my Utica gas furnace entailing a single outlet so I can run my generator to it in case of a power loss….it seemed straight forward, i found the breaker that powers off the burner, also observed in the breaker box that my wiring to the breaker was aluminum(2 wire black white ground @12gauge/20 amp) opened the honeywell side mounted box to get to the power wiring at the furnace, and this is where I stopped short….looks as if the power line coming in to this box has 3 wires not 2…it seems to have 3 -12 gauge aluminum wires..red, black,and white….red wires to the board#1 terminal to the transformer and the white also goes to terminal # 2 on the board to the transformer for a step down 30 vac for the thermostats….the black wire is wire nuted to another black and runs off to the possibly the circulator side of the furnace…my question is what do i do with the red wire when seperate the power line and install a single outlet?

    1. Hi John! I am sorry, but I have never encountered this wiring situation before. You might have an electrician advise you on this. I am afraid that I might advise you wrong. When I hear about 3 wires red, black and white I think you might have 220 volts. Between red and black would be 220 to 245 volts and between red to white and black to white would be 120 volts. I suggest you check this with a volt meter to see. I am very sorry that I can not give you any advice on this. I hope someone will see your question and advise. I hope you have a nice day! Steve

  11. Hi, I have a International Comfort Product (ICP) HVAC system installed a little over a year ago. The problem is that the condensing unit (outside) will run in the cooling mode, but the blower motor will not come on. Thus freezing up the inside coil, the HVAC Tech has been out numerous times for this problem. Once he found a blown fuse, the last time this happened the fuse was good and he could not find the problem, do you have any suggestions what could cause this, thank you in advance?

    1. Hi Mr. Longmire! I will start with the simple thing first. Please make sure if your thermostat has batteries that the batteries are good. When the blower does not come on you will need to tape the blower door safety switch closed so you can test the furnace with the power on. With the AC calling for cooling, set your volt meter to “Volts AC”. Test between the G and C (com) terminals you should have 24 to 28 volts AC between these two terminals. If you do not then you have a thermostat problem or a thermostat wire problem. If you are getting 24 volts between G and C and the fan is not running then you either have a control board problem, fan blower motor problem or a blower motor capacitor problem. I would suggest making sure all connections are good and tight. If you have a high efficiency ECM blowe motor then I would leave this to a qualified tech to check the motor out. It takes special tools to analyze ECM motors. I hope you can easily find and fix the problem. If you have a part that needs replacing it should be under warranty since the unit is only a year old. Sorry you are having problems! Steve

      1. Thank you Steve, the HVAC took the batteries out because they “weren’t need” anyway, my background is HVAC that’s what I did when I was in the military, but haven’t dealt with it for a few years. You’ve given me a wealth of great information, Steve, you are the Man, I can’t thank you enough!

      2. Hi Mr. Longmire! Thank you so very much for your military service and kind words! I sure do appreciate your nice comments! God bless you and your family today and always! Steve

  12. Hi,
    My air conditioning unit failed at the end of summer. It’s a split system and I noticed the R22 was let out somewhere near the bottom of the compressor. Someone came to see it and determined that indeed there was a leak; he didn’t really figure out the location and was more concerned about selling me a new unit (pair)..At the time $ was an issue for me and we roughed it with fans. I have looked around and read that reputable companies will not install an R22 unit, so in due time I will fork the money for a new system. Now it’s cold, so in the meantime I’m wondering if it’s safe to run the heater. Thanks in advance for your advise.

    1. Hi Jose! Yes, you can run the heater, but I would not recommend running the outdoor unit at all. If you have a heat pump I would recommend going to emergency heat on the thermostat which should not allow the outdoor unit to come on and you will be using all auxilliary heat for your heat source. It would not be good to run the outdoor unit if you are out of or low on refrigerant. Yes, this is true. They are phasing out R22 units so you will need to replace both the outdoor unit and the evaporator coil with new equipment using the new refrigerant R-410A. Steve

  13. Hi, I recently had a Rheem direct vent furnace installed with 2″ PVC with an approx 30′ run to exterior. I was then told by an inspector that it needs it to be 3″ not 2″ PVC. Is this true? Will there be issues with my unit if I don’t change it?
    Please advise.

    1. Hi Ms. Weaver! Thanks for asking this question. It would depend on what the installations instructions are for your Rheem furnace say. In the installation instructions (every furnace should have this with a new furnace) the manufacture will have recommendations on what size vent pipe and how many 90 degree turns are allowed. If the furnace is not installed according to the manufacturer’s recommendations you might start having trouble with the pressure switch not allowing the furnace to operate and the furnace will lock out. You will know pretty soon if the vent piping is not adequate because the furnace will stop working. I would call your installer and tell him what the inspector said. I remember I had trouble where I installed too small of pipe (2″) and I had to go back free of charge and replace the 2″ pipe with 3″. I learned alot from my mistakes and I never want to make that mistake again! Ha! I hope that your furnace was installed according to manufacturer’s recommendations. Steve

  14. Steve, I have a rheem gas furnace/AC unit . It sits right outside my house. I suddenly heard it running loud tonight. The fan on the unit wasn’t running. I cut the thermostat down, the system cut off. So the thermostat is working ok. Is the fan always supposed to run when the motor is running? I don’t smell gas. I am afraid to leave it running and do any damage. I have had it 10 years. What might be the problem? Is there something I might check without having HVAC exp.?

    1. Hi Ms. Avon! If you have a unit that is a heat pump with gas as an auxiliary heat source then when a heat pump goes into defrost mode the outdoor fan will stop, the reversing valve will shift into cooling mode, auxiliary heat will come on and the ice which has accumulated on the outdoor coil will be melted off. Many times when this happens homeowners of heat pumps will hear loud noises and see hot smoke from the melting of the ice coming off their outdoor units. I have had customers call me thinking their unit is on fire! So if you have a heat pump then what you heard might be normal. Usually after the ice is melted (3 to 10 minutes) the heat pump will start back up and sound normal. If you do not have a heat pump and the fan is cutting off then I would suggest checking the fan motor capacitor to make sure it is not weak and in good shape. Many appliance parts stores will test capacitor for free. This could also be a fan motor problem where the motor bearings are getting tight and the fan motor is over-heating. If this be the case then you will probably need a new fan motor. A faulty fan relay on the control board can also cause fans not to run. You might need a new control board if this is the case. I hope you can easily find and fix the problem if you have a problem. Merry Christmas! Steve

  15. Hello. I have a Rheem RBHP-24J18S air handler that has me pulling my hair out. One night I noticed only the blower was running with no heat coming out of the vents. The next day I climbed in the attic to check things out but didn’t notice anything out of the ordinary. After some research I noticed the most common problems were sequencers, control board, and thermostats. I actually had a new thermostat and control board for a spare so I changed them along with the sequencers. Then set the heat on auto to start the cycle and the blower came on and a few seconds later the air began blowing out the vents harder and warm. Everything seemed to be worked fine but a few minutes later the air flow slowed down and it was blowing cool air. I went back to checking things and found the defrost control switch was failed open so I changed it along with the watt restrictor switch. Now I don’t get any heat at all just seems to be the blower blowing cool air. I checked both sides the transformer and getting 24V and 240V and getting 24V going to the control board. I also noticed after turning on the AC that after the cooling cycle is over and the compressor shuts off the blower continues to run for a minute or so…like the heater should do after the heating cycle is complete. Any help solving this would be GREATLY appreciated!

    1. Hi Jaron! If your electric furnace or heat pump is not having any heat come out of the registers it is probably a sequencer, control board or limit that has gone out. The white wire off the W or W1 connection of your thermostat should be energizing the electric heat when the thermostat is calling for heat. I would suggest testing with a volt meter to make sure the thermostat is energizing the W and C (com) terminals on your control board. If it is then I would suggest testing to see if you are getting 220 to 240 volts to the electric heat elements. This can be dangerous since you are working with live electricity high voltage. You might want to call in a tech to troubleshoot. I always liked troubleshooting electric furnace’s with an amprobe which shows the amps running through the wires by just clamping around the wires. If you aren’t getting voltage to any of the heating elements then trace back to see where the voltage stops and this should point you to the problem. I sent you a PDF parts list for your furnace with drawings to the email address in this post. I hope this helps you finding and fixing the problem. Steve

      1. I’ve already changed both sequencers and control board. I also checked for continuity on the 5 limit control switches and they seemed good. When it was working for short periods I found the defrost heater control switch would fail open and it would go into “cool down mode”. That is why I changed the that switch but since I did only the blower is coming on. On my unit the W wire from the thermostat connects to the purple wire for this defrost control switch with a wire nut and then comes out the switch and connects to the bottom of the first sequencer. Where should the W wire connect to…the W1 on the control board?

      2. Hi Jaron! Hopefully you have a wiring diagram attached to the furnace blower door or somewhere on the furnace. I would suggest following the wiring diagram. Sounds like the control board is not doing what it is supposed to do. Sorry that I can not give you an answer to your problem. When I was doing service I would tell myself, “if the power is going into the control board or other control and not coming out then the control board or other control is the problem”. I hope you can find the problem. Steve

  16. hey I have a ruud heat pump with auxiliary heat strips. Everything works normal until I turn on the emergency heat. The heat strips come on but not the blower. The blower won’t come on even if I turn it from auto to on. What could be the problem?

    1. Hi Chris! This could be a thermostat problem where the thermostat is not telling the blower relay or sequencer to come on when the thermostat is set to emergency heat. I would suggest testing to make sure the “G” connection (24 volts between the G and C com) on the thermostat is being energized when in emergency heat. If it isn’t then you have a thermostat problem and if it is sending 24 volts to G then you might have a fan sequencer or relay problem. I hope you can easily find the problem. Steve

  17. I have a down draft Payne gas furnace. It is 26 years old. It has started short cycling.
    If I turn the furnace off and then on at the furnace. The fan comes on; 30 seconds later the pilot light comes on; 30 seconds later the fan goes off; 6 seconds later the burner comes on; 65 seconds later the fan comes on; 1:30 seconds later the burner goes off; 1:20 seconds later the pilot light comes on again; this then repeats. Fan off; Burner on; Fan on; Burner off; Pilot on; Fan off; etc.
    I replaced the previous HH84AA Fan Control Module (Fan would not shut off) with a replacement ICM271 Fan Control Module awhile back. I bought two. I just replaced it again with the second one. No change in cycle.
    Note: The Fan on / auto switch does not work on the Honeywell Thermostat Controller. The fan does not turn on.
    Note: It is cold outside. The Honeywell shows heat on all the time.

    1. Hi Mr. Goodwin! It sounds like you might have a thermostat problem. I would suggest that your check with a volt meter set to “Volts AC”. You might have to tape your blower door safety switch down so you can test the furnace with the furnace door off. Set your thermostat so the heat is on and check with your volt meter between the W and C (com) terminals you should be getting 24 to 28 volts AC between these two terminals until the temperature that is set on the thermostat is achieved. If the voltage cuts out when the gas goes off then this is the thermostat cutting the gas off. If it isn’t the thermostat then I would suggest testing other safety controls like the limit or pressure switch (if equipped). We have a troubleshooting flow chart that I hope will help you out on the following page: https://arnoldservice.com/furnace-trouble-shooting-flow-chart/ I hope you can easily find and fix the problem. Steve

  18. My blower fan will not shut off in the auto mode of either heat or cool setting. It just keeps running. I was told to tap something lightly with a hammer in the furnace, but that didn’t do anything. Could my honeywell thermostat be bad? We have been moving the thermostat switch to off and then turning off the blower by using the main blower switch on the side of the furnace just to give the blower a rest.

    1. Hi Jerry! You either have a stuck relay on the control board, a thermostat problem, thermostat wire problem or a limit that is open. We discuss this problem on the following page: https://arnoldservice.com/problem-your-fan-on-your-furnace-runs-all-the-time-and-will-not-shut-off/ I hope this helps you find and fix the problem. Steve

  19. Hi, I have a strange issue that you may have addressed above but it doesnt match to any Q&A 100%. I have a honeywell/becket furnace connected to insteon smart thermostat. This year it started to behave strangely:
    when the temp is set to higher end (73+) when it reaches 73 the power to thermostat drops to 0 for 60 seconds.
    Thermostat shuts down and then reboots when the power is back.
    I have used volt meter immediately after thermostat turns off and it shows 0. During normal operation it shows 27V AC.
    I have also used volt meter down at the furnace C&R (matching the thermastat) and it also shows 27V going to 0, and then 60 seconds later everything comes back.
    I am about to go out to and try new thermostat (honeywell) to see if it helps, but something tells me that it may be a problem with furnace/transformer?

    Any suggestions?

    1. Hi Dave! Yes, from your description it does sound like a transformer issue or a loose wire on the primary or secondary side of the transformer. On many furnaces the transformer is connected directly to the C (com) and R terminals on the control board. Some transformers have an in-line fuse in case of a short it does not burn all the low voltage controls up. I would also suggest that you check for a loose fuse if the furnace is equipped with a fuse. I think you hit the nail on the head with the transformer or a loose wire being the problem. I hope you can easily find the problem and get it fixed. Steve

  20. Steve,
    I have a hot water coil on my return side of my air handler unit that I use when burning wood. I had an older air handling unit that I simply opened and closed the green wire to use the fan in the past. I now have a new system with a V.S speed fan and 24v control. (Bryant) controller. How can I run the fan at max speed while circulating hot water? I am thinking I may have to put in a relay with a separate voltage source to fan motor but would prefer to use existing control system.

    1. Hi Mike! Usually variable speed motors have dip switches that you can set for different amounts of air flow. The dip switches are usually located on the controller. If you do not have the dip switches then I do not know what to tell you. I would be afraid to hook the motor directly up to 120 volts AC because some of the high efficiency motors are ECM DC motors. I would check with the manufacturer before wiring up directly to 120 volts AC. I hope you have a nice day and weekend! Steve

  21. recently I had AT&T installed AT&T digital life system. The installing tech said was unable to install the thermostats because the voltage coming to the thermostats is too high, reading 27,28. I had two HVAC companies come and look at the system and they tell me that what I have is standard and can’t change it. I paid one of them to change the transformer on the furnace to 24 volt. Even with that the volt reads 27,28. Anyone had this problem? The thermostats are “DLS Thermostat 2.0” they are still in their boxes not installed.

    1. Hi! Most heating and air thermostats when a load is not applied register between 24 to 28 volts AC. This is normal. The thermostats should work with this voltage if the AT&T digital life thermostats are designed to work with a 24 volt system. I would try to contact the manufacturer of the thermostats and ask them if it would harm the stat if they receive 27 volts. If they say, “Yes” then I would look into returning the thermostat and getting a thermostat that is not so sensitive with the voltage. Steve

  22. Hi,

    The control panel in my furnace has a small brown mark like a burnt mark, does it need to be changed?

    1. Hi! Brown marks on control boards indicate excessive heat which is caused most of the time by arcing. If the board is still working properly I would not suggest replacing it. I would suggest making sure all connections to the board are good and tight. Any loose connections can cause arcing and excessive heat. Thanks for asking this question. Steve

  23. I have a 5 amp control fuse blowing in my furnace, killing the themostat. if I set the themostat to fan only it does not blow. I turned off power to my heat pump and set themostat to call for cool and the fuse held and the contactor kicked in. The starter capacitor is ok. Put the unit back together and ran fine for 10 minutes then blew the fuse. Any advise what to do next?

    1. Hi Mr. Taylor! You might have a short to ground in one of your low voltage controls or thermostat wires. Please check and make sure all your low voltage thermostat wire connections are good and tight. A loose connection can cause high amp draw and blow a fuse on the board. This should not have anything to do with the high voltage side on your unit such as the capacitor. We discuss this problem on the following page: https://arnoldservice.com/problem-furnace-air-conditioner-heat-pump-will-not-come-on/ I hope you can easily find and fix this problem.

  24. My Aunts ac is having an issue with the thermostat. Twice now within a month I have had to replace the batteries. The outside unit runs but, the blower won’t kick on. The outside lines get ice on them, I replace batteries wait a few minutes then turn to auto and both come on and work fine. Is it the thermostat going bad and eating batteries, or is there something more?

    1. Hi Duane! This sounds like a thermostat problem or a blower motor problem. The next time that the blower will not start I would suggest turning off the power to your furnace or air handler and lightly touch the blower motor to see if it is hot. If the motor is pretty hot you might have a blower motor problem (might need a new motor) or the motor might need a new run capacitor. Weak run capacitors can cause motors to run hot and stop running when they go off on thermal over-load. If the motor is not hot then I would suggest that you open the thermostat up, loosen the red and green wires on the thermostat, turn the furnace power back on, and touch the green (G) and red (R) wires together. The blower motor should start. If the blower motor does not start then you have a thermostat wire problem. Please make sure all thermostat wires are good and tight because a loose wire can cause high amp draw and run your batteries down. If the blower starts when you join the Red and Green wires together and you do not find any loose wire connections then I would suggest a new thermostat. Maybe one of the relays inside the thermostat are arcing and causing the high battery draw. Best of luck in finding and fixing the problem. Steve

  25. Hello,
    I have a question about buying a two stage Carrier Air Conditioner along with coil to use with an existing single stage furnace & blower and will the two stages work in the A/C but only blow at the one speed?

    1. Hi Jim! I called my Bryant Carrier supplier and they said that you could install the two stage Carrier AC with a single stage furnace, but the AC (outdoor unit) should only work on one speed. Then if you ever want to install a two speed furnace you could take advantage of the two speed air conditioner as well. So they do not recommend utilizing the two-stage AC with a single stage furnace or air handler. I hope this answers your question. Hope you have a great day! Steve

  26. Question: We bought a place and there was a note that stated to turn the a/c breakers off when switching to heat. No issues but when I installed a new Sensi thermostat when I turn the a/c breakers off the heat doesn’t work. When I turn them on the heat kind of works but the outdoor condenser unit is running. What could be the issue? I wired the new thermostat just like the old one. Thanks J

    1. Hi Justin! Sounds like you either someone wired the system wrong, some thermostat wires are shorted out and causing the outdoor unit to come on or you have a heat pump unit where as I am sure you already know that heat pump units run in the winter time. I have no idea why they would have a note to switch the breakers off when switching to heat. We have a post with YouTube videos on thermostat wiring that might help you out, but you probably already know this: https://arnoldservice.com/problem-i-purchased-a-new-programmable-thermostat-my-thermostat-wiring-only-has-only-three-wires-the-thermostat-instructions-call-for-a-red-power-wire-a-yellow-green-and-white-wire-my-three-wire/ You or a tech would need to troubleshoot and study how they have your unit wired and figure out what they did wrong in the wiring. I have a Sensi Wi-Fi thermostat and love it. I am sure that when you figure out what they did with the wiring that you will like the Sensi thermostat as well. I hope you can easily find and fix the problem. Steve

  27. My home warranty company has determined that the compressor in my Carrier condenser (4-ton, model 38TKB048350, built in 2003) has burned up and needs to be replaced. The contractor that came out is trying to order a Rheem 4-ton compressor to replace the Carrier compressor that came in the unit. The Rheem compressor is very inexpensive compared to the Carrier replacement part ($300 vs $1,100), uses 4 additional pounds of freon (11 vs 7). I have been told that a compressor is matched to the condenser and the evaporator coil and that the compressor should be replaced with a Carrier authorized part or the system may not perform as expected. Would it be acceptable to allow them to use the Rheem compressor? Is this normal practice, or just a way for the home warranty company to cut costs?

    1. Hi Charles! I personally would always want an OEM compressor made by the manufacturer. That being said, many manufacturers use the same compressors in their equipment. Copeland makes many of the scroll compressors like your unit has in it. If your home warranty contractor is using the same Copeland scroll compressor as what came out of your existing unit then I would say this would be A-OK since you are getting the same compressor installed. Our Carrier parts program shows a compressor part number SRD480HC scroll compressor. I feel that scroll compressors are about the best you can get. I would make sure they at least replace your compressor with a compatible scroll compressor. I would not accept a reciprocating compressor. I hope you get this worked out soon where you are treated fairly. Steve

  28. I’m getting ready to replace my 22 year old York heat pump with a Trane XL 16i. It’s 3.5 ton and services a quad-level home. The contractor wants to eliminate the outside electrical box. I think it’s a high voltage fuse? I’ve never seen this done. He says it will go directly to my house electrical panel. Is this acceptable?
    The other problem is that he wants to put salt-treated lumber to support the air handler in the crawl space and on the outside pad for the condenser. I live in a high humidity hot summer and cold ice and snow winters. I just can’t imagine using wood instead of concrete block. Otherwise, they have good reviews, but it sounds really weird and temporary to me. I have rotting landscape timbers right now in my back yard. The crawl space is sealed, but not conditioned. Duct work is in crawl space. Does lumber sound right for this application?

    1. Hi Jennifer! I would suggest that you make sure the contractor gets a permit for the installation to make sure the installation is inspected and done to code. Here in Louisville, KY all outdoor units must have a disconnect box so a service person or homeowner can easily disconnect the power to the outdoor unit. I do not know what your code is, but I would think they would want a disconnect box for the unit. Again, on the salt treated lumber I would check with your local HVAC code enforcement to see if this is allowed. If it was my home I would prefer a concrete pad just because of the looks. I think concrete would look more professional. You can tell the contractor that you want him to get a permit because you could have trouble selling your house in the future if a permit is not acquired for the installation. When I installed my own furnace and AC at my home I paid to get a permit so there will be no questions asked when I want to sell our home in the future. Thanks for asking these important questions.

  29. This is just a solution I found on those 2 stage gas valves controled by a thermocouple and a thermopile . I have a propane fireplace and it hadn’t been used for a few years . It wasn’t very old and had few hours of usage . I had a new propane tank installed and went to lite the pilot and it wouldn’t stay lit . Was ready to buy a new gas valve but decided to give the whole log set a good cleaning so out it came . I vacuumed and rubbed and polished and wiped down the thermal-couple , put it all back together and it worked . The coating of residue on the thermal-couple bulb was keeping it from putting out the required micro-volts to keep the main valve open . A good cleaning once a year might save someone a few bucks and it might be a solution to some of those dual fuel heat-pumps not lighting or staying lit ..

    1. Thanks for sharing your information about fixing your propane fireplace! I hope your post with help others with a similar problem. Steve

  30. My A/C unit is a year old. Problems began recently when I would come home from work and my house would be HOT even though I left the A/C on. The thermostat was set to “cool” but warm air was coming from the vents. I have had two repairmen come out and when they leave I think the problem is fixed only for the problem to occur again a few days or a few weeks later. I began to think it was the thermostat, but one repairmen claimed my thermostat is fine. This past weekend I changed the temp on my thermostat from 74 to 78 and I heard the unit turn off. About 10 minutes later, I heard the unit come back on! I went to the thermostat and it did not indicate the unit was on. I moved the thermostat from “cool” to “off” and the unit still would not turn off! I also began to notice a burning smell. I took the face of the thermostat off the wall and the unit turned off. Is it possible that the thermostat would cause this to happen? Or could it be bad wiring? Or the transformer? Again, I have had two repairmen come to my house and make “repairs” and take my money but the problem has only gotten worse. I just need to be pointed in the right direction. Thanks for any help.

    1. Hi Deon! Sorry to hear you are having this problem with a fairly new unit! This sounds like a thermostat problem or some thermostat wires that could be shorting out and causing the unit to start on its own. This problem can be hard to find, unless you can troubleshoot the problem when it occurs. I would suggest the next time the outdoor unit comes on when it is not supposed to that you test with a volt meter set to “volts AC” between the C (com) and Y (usually a yellow wire) on your furnace or air handlers control board. If these two connections are receiving 24 to 28 volts with the thermostat not calling for cooling or with the thermostat turned off then you either have a bad thermostat or some of the thermostat wires are shorting together causing the outdoor unit to come on. You could also try disconnecting the Y wire from the thermostat and see if the unit outside stills runs. It should not run with Y disconnected. If it does run then you do not have a thermostat problem, but some shorted thermostat wires or another control that is causing this problem. I feel it is probably the thermostat. Best of luck in finding and fixing the problem. Steve

  31. Hi, I have enjoy the information I have been reading with in your website, great job, my question is: I believe I have some plugged capillary tubes or orifice’s, I have a low suction pressure, and high head pressure, I was wondering if you had any thoughts or experience with the product from nu calgon called AC Renew, it is supposed to help lubricate the compressor system while helping to break down the burnt oils that cling to the inside of the tubing. Here is the video from YouTube https://m.youtube.com/watch?v=Lbg2awS-RRM,
    Just wondering your thoughts or if you have had any experience with this product, my system does not have a txv

    1. Hi Regan! Yes, if you have high head pressure and low suction pressure then you probably either have a stopped up cap tube, bad TXV valve, dirty condensing unit or a slow condenser fan motor. I have never used the AC Renew, but I have seen many of my suppliers selling it to prevent sticking TXV (thermostatic expansion valve) problems. I heard there is a problem with the compressor oil reacting with the TXV valves. I heard the AC Renew is good to prevent the TXV Valve from having problems, but I believe once there is a problem with the TXV then it is must be replaced to cure the problem. One of my suppliers said there was a recall on the TXV valves and after replacing the valve the manufacture was recommending the AC Renew product to prevent it from happening again. I hope this helps you out. Steve

  32. I have a goodman ac/heating unit 13 seer gsx-gmh 5 ton installed 2012. What fine for 3 years 10 months then the flame sensor needed to be replaced.
    The havc tech installed a new sensor worked fine for 1 day then the unit started to vibrate followed by a loud rattle sound. Havc 2nd visit tech did not have a clue what was causing the problem. Hvac 3rd visit different tech.The loud rattle noise was noticable tech determined it was the gas line. Tech tighten the unit that solved the loud rattle. Tech did not have any idea what was causing the vibration. The vibration at times is excessive. The unit is installed in the attic and when it vibrates you can see the cables and gas line wobble at times. This all started with the flame sensor being replaced.
    Could it be the blower, fan, wheel, bearing etc. need adjustment or alignment. The current decibel reading when running 70-78. My question is what can cause the unit to vibrate and at times excessive vibration?

    1. Hi! Most of the time vibration is caused by an off balance blower wheel or like you say a loose blower motor bearing. In my experience most of the time the vibration is caused by a piece of paper or debris that has been sucked up into the blower wheel and causes it to be out of balance. I have seen other vibration noises on Goodman units that are caused by having loose heat exchanger mounting brackets. These brackets help hold the heat exchanger in place and it they become loose they can rattle and make lots of noise. I would suggest turning off the power to the furnace and taking a mirror so you can inspect the blower wheel to make sure something has not been sucked up into it. Best of luck in finding and fixing the problem. Steve

  33. My a/c is not blowing cold air, it is blowing room temperature air (so not hot), but definitely not cooling down the house. The compressor runs, but the pressure does not change when switched from off to on. The capacitor appears to have been spent by this. I am trying to diagnose whether this is a valve issue (that can be fixed), whether the compressor needs to be replaced, and if the compressor needs to be replaced whether the refrigerant (currently R 22 on a 10seer unit) also must be replaced. Local HVAC companies are trying to charge me 8K+ to replace the entire a/c. To complicate matters, replacing it would be difficult given limited roof access (requiring a crane) and limited space (contractor put all these old units really close to one another). Most of these companies do not seem to want to actually diagnose the problem so I’m trying to figure it out myself (but will of course hire a licensed professional to do the actual work). Any suggestions?

    1. Hi JS! If this is an older unit more than 10 years old it should use R22. It should show what refrigerant the unit uses on the outside label of the unit. If the air coming out of the vents is not cool I would suggest hooking up gauges to the unit and see if the compressor is pumping or not. The gauges will show whether the unit is low on charge, has a bad valve and whether or not the compressor is working properly. If it is a bad compressor you should be able to purchase a new R22 compressor and have it installed. The most important thing to find out is what caused the compressor to fail in the first place. If you want me to look up parts please send me your unit’s model number and I will see what I can do. Best of luck in finding and fixing the problem. Steve

  34. I have a Carrier unit about 8 yrs old. The indoor blower fan stopped working. I took panel off to see if I could see anything . I noticed that when i turned breaker back on one of the two heating coils under the fan comes on and stays on for a minute then clicks off, even while in A.C. mode. I was told to check the sequencers, one might be stuck. I dont have sequencers but i do have 2 relay type things, looks like one for each coil? I was told the one for that coil that kicks on could be bad which would make fan not work becsuse its not getting the right signal. Wondered if this sounds right to you too? Please help asap!!!. Thank you so much!!!

    1. Hi Jason! This could be the possible problem. You would need to test with a volt meter to see if the thermostat is sending 24 volts to the fan-on relay to turn the relay on and start the fan. You should be getting 24 to 28 volts AC between the green and C (com) wire when the thermostat is calling for cooling. If you aren’t getting 24 volts between G and C then you might have a thermostat problem. If you are getting 24 volts between G and C and the blower motor is not coming on then I would test the low voltage going into the fan relay. If the relay is getting 24 volts and not sending the needed 220 volts to the blower motor then you probably have a bad relay. If you want to send me the unit’s product number I will try and look up the part number for the relay. Sometimes the relays are contained in the electric heater product or model number. So I would need the heater model number to look up the parts. I hope you can easily find out what the problem is. Steve

  35. If I allow my electric utility company to cycle my home a.c. every 15 mins. on/off do I risk a.c. compressor, contactor,controller or any other componant to fail any sooner than if I just run as normal (let unit cycle normally)???

    1. Hi Rich! Great Question! Our utility company, only cycles the Air conditioning equipment off and on once or twice a day during peak electrical usage times. It isn’t every 15 minutes. If your utility company is cycling your AC off and on every 15 minutes then this seems like it would be going against what they are trying to accomplish which is reduce the load on electrical usage and to reduce the strain on the utility company’s equipment. Starting AC equipment is hard on the system because it jumps the amperage/electrical usage up each time when AC equipment starts. If your utility company is starting and stopping your equipment this often it does place more of a strain on the compressor, contactor and electrical components in your air conditioner and I would not want to sign up for something that does this. If they cycle your AC once or twice a day then this would be OK. I hope I have answered your question. Steve

  36. Hello. I was told that my outside AC unit and the Coil in my attic needed to be replaced. When trying to get the new coil in and the old coil out, it was discovered that the access to my attic was too small for the for them to get through the access door. I had a contactor come out and they said they are unable to widen the access door because it would require cutting one of the trusts that are holding up my roof. they look at other spaces in the attic but determined that there was no other spot that they would be able to cut open a hole large enough to get it in the attic. I googled that question and saw one person type a response that stated “the coil can be removed from its drain pan, the cover sheet/plates removed. and the coil can then be squeezed together some to make it fit through the attic access. they said they’ve done it many times to coils and have disassembled many air handlers to get them in the attic. Is this something that truly can be done? Or do you know of any other options? Please let me know. thanks.

    1. Hi Shawn! Sorry to hear that you are having this problem with fitting the air handler into your attic. It would depend on what type of brand name air handler that you are installing. I would ask your contractor to look for an air handler that can be disassembled in pieces then reassembled in the attic. Another idea would be to only replace the evaporator coil and not the entire air handler. You should be able to find a coil replacement given the measurements of the old coil and the BTU. rating of your outdoor unit. That is about all the advice I can think of if they can not make the access hole any larger. I hope you can get this worked out. Steve

  37. Can you please answer this question for me? I would ask my local HVAC guy but he didn’t respond to two calls. In the attic is an air handler that has not worked for over 6 years, maybe more. Research results say to have an EPA certified technician remove the refrigerant before anyone can disassemble the unit. Another source states that to evacuate the refrigerant the unit should be running. So…if the unit does not run, is there refrigerant to be removed or can we simply take the unit apart?

    Thank you so much.

    1. Hi Mr. Judd! Thanks for asking this important question! The right answer is to have an EPA certified technician to remove the refrigerant before anyone can disassemble the unit. If the outdoor unit has already been removed and there is no refrigerant in the system, then you would not need to call in a technician to remove the refrigerant. It is a $10,000.00 fine if EPA catches a person releasing the refrigerant into the atmosphere because this is so detrimental to the environment. If both the indoor and out door units are attached then there is probably refrigerant in the system and it would need to be removed by an EPA certified technician using a refrigerant reclaimer. The reclaimer is attached to the system and it sucks the refrigerant out into an EPA approved refrigerant reclaiming tank. When the tank is full the HVAC tech should take the reclaimed refrigerant tank to a refrigerant reclaiming facility where they reclaim and process the refrigerant to be used again. The refrigerant at the reclaim facility is tested to make sure it is good refrigerant and not mixed with acid. If the refrigerant has acid in it the technician has to pay for the refrigerant to be processed. If the refrigerant is good then many times the technician will receive money for the refrigerant. All of this has to be documented by the technician and the reclaiming facility. I hope that I have answered your question. Steve

  38. Hi! I have a problem with a furnace (located in a ceiling attic) that loses power when it gets very hot outside, say over 100 degrees. This happened last year a few times, this year it is much worse – is happening daily. I’ve checked the breakers, the float valve, and everything seems fine. I’ve also replaced the fuse on the furnace board, and it doesn’t make a difference. The thermostat will go completely dark in the late afternoon and then light up again some time later in the evening when it cools off. We think it is heat related because that is the only pattern visible. Flipping breakers doesn’t bring it back to life.

    AC man came out today and talked to my wife, he claims we lose power to the furnace because the outside unit overheats. I’m skeptical because it seems even if the outside unit could not run, why would that prevent the furnace & thermostat from receiving any power? I was really hoping it was the float valve given there is some water in the pan but that valve seemed OK. Interested in any ideas!

    1. Hi Paul! Sorry to hear you are having this problem. It is obvious as you say that the thermostat is losing power. This could be 24 volt power or 110 volt power. If the whole furnace or air handler is losing power then this would cut the low voltage power off to the thermostat as well. The only way that I would know to tell what the problem is would be to test the different connections and terminals when the problem occurs. I would start with the float switch, the door switch on the furnace blower door, the air handler or furnace control board testing between R and C (should have 24 to 28 volts AC). We have an AC troubleshooting flow chart that I hope will help on the following page: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf This will be difficult to troubleshoot unless you can troubleshoot when the problem occurs. I hope you can easily find and fix the problem. Steve

    2. please, check if you have a condensate overflow switch on the unit. If you do, check if your condensate line is clogged. You can check that by pulling the top of the switch out of the T fit ting. The level of the water should no be higher than the center of the T otherwise the switch activates and shuts down your AC. The switch is a safety against water overflow. When you pull the switch out, let it hanging down and the unit will start up. Then you know there is your problem, clean/unclog the condensate drain line, place the switch back on the T fitting and “magic” !! All good. Make sure the drain line stays unplugged.

      I hope this helps.


      1. Thank you so very much for telling us how you solved the problem! I hope this help others out! Steve

  39. My Heat Pump stopped working last January, and suddenly began making a horrible noise (during one of the coldest times I remember in my area). I had someone out to service it the following day. What I learned was that this well-known, established company, who had replaced my “outer blower motor” 5 years earlier had removed a wiring protective tube (that came with my unit) where the 220v wires were supposed to be run – and had directly zipped tied them to my copper discharge tube. The wire shielding on these wires had worn away (Heat?/Vibration?), exposing the 220v wires, it then arched, immediately blew-out my outer blower motor and blew a hole in my copper discharge tube allowing all the Freon to escape; thus a dead system. I was told it was a 50-50 decision on my part to either repair or replace. I got 3 other quotes. All of them told me basically that my problem was a direct result of this blower motor install years earlier. [Note: I wish there was a way I could upload photos because they all took photos, so I have some good ones]. Every person (all professionals) told me “Your problem is a direct result of their install. It wasn’t a matter of ‘IF’ this would ever cause a problem, but ‘WHEN’.”

    I’m not a heat pump person. My question is “Does what they said make sense?” –tim

    1. Hi Tim! I am so very sorry to hear that someone did bad work which resulted in your heat pump failure with lots of lost money, heat and air conditioning! Yes, wires that were not secured properly and touching refrigerant lines is bad work. I would suggest calling the company that did the bad work and ask them to replace the unit free of charge. I would not repair this unit because if the unit ran anytime with the hole in the refrigerant lines then this contaminated the whole system with air dirt and moisture. I am very sorry for your time and trouble. Steve

  40. I had a capacitor replaced for each of my Air Conditioning units. the Tech guy gave me the old ones and told me not to touch the prongs. I left aside and forgot to tell my wife. She touched the prongs not knowing. i did not get an explanation from the tech what are the consequences and what are my actions when that happens. Can you advise?

    1. Hi Victor! The consequences might be an electrical shock. If you wife did not feel an electrical shock then the capacitor must have been discharged and there is nothing to worry about. We have a page dedicated to “How Do I Discharge a Capacitor” https://arnoldservice.com/problem-discharge-high-voltage-capacitor/ I have never been shocked by a capacitor, but I know guys who have been shocked and it is an uncomfortable feeling! I hope you have a nice day! Steve

  41. hello…my rv a/c compressor is not coming on or when it does i can tell that is running very slow. I changed the run capacitor and added a hard start to it thinking this is what was needed. It made no difference. When I checked the old cap it registered good. What could be the problem?

    1. Hi Mr. Thibodeaux! If you AC is not starting or running slow this could be caused by a low voltage drop across the contactor, generator or power cord that is connected to your home to power your RV. I would suggest checking the voltage drop to make sure you are getting at least 110 volts out of your generator or home AC electric service when the AC compressor tries to start up. If the voltage goes down below 110 volts then you will need to increase the output of your generator, use a larger power cord (10 guage) or you might need a new contactor. This is the only thing that I can think would cause the unit to run slow or not start at all. I hope you can easily find and fix the problem. Steve

  42. I got a Bryant one piece unit and the blower will not come on you can turn it on manual on the thermostat but it runs low speed but doesn’t turn on with ac or heat high speed

    1. Hi Dennis! I try to discuss this problem on the following page: https://arnoldservice.com/problem-fan-will-not-come-position-fan-will-not-come-turn-thermostat/ Since your fan is running at low speed some of the time I would suggest that you check the thermostat to make sure you are getting 24 to 28 volts AC between the G (green) and C (com) terminals when the thermostat is calling cooling. If you aren’t getting 24 volts between these two terminals then you might have a thermostat problem or a thermostat wire problem. If you have batteries in your thermostat make sure they are in good shape. Please make sure you check the blower motor capacitor to make sure it is in good shape. A weak capacitor will cause a motor to not run. Check to see if you are getting 110 to 125 volts AC to the blower motor when the thermostat is calling for cooling. If you aren’t then you might have a control board problem. Check to see if the blower wheel spins freely. If it doesn’t then you might need a new blower motor. Lightly touch the blower motor to see if it is hot. If it is hot you might need a new capacitor or a new blower motor. Best of luck in finding and fixing this problem. Please send me your furnace’s product number if you would like for me to look up parts. I hope you have a great day and week! Steve

  43. Hiii
    My question is can I stop the hvac for some time. If some reasons we may want to stop the hvac for some time (minutes or hours), how much time should I stop…
    Few days back we noticed water leaking from hvac, our maintenance people said that, u should have to run your hvac continuously. Can I stop hvac…

    1. Hi! You should be able to stop and start you air conditioner when ever you want. I would recommend waiting at least 5 minutes in between cycles so the refrigerant has time to equalize before restarting. The maintenance people may have wanted you to run the AC all the time (blower all the time) if you have a low refrigerant problem or a low air flow problem to keep the in door evaporator coil from freezing up. Running the fan all the time would help prevent the coil from freezing up. Please make sure that your filter, blower wheel and evaporator coil are clean. Please make sure the capacitor on your blower motor is in good shape. If the capacitor is weak the blower motor will run slow. I hope that I have helped answer your question. Steve

  44. I have a question. I have a AC overhaul being done at my house today – not there so the repair guy relayed a message to my daughter. They are replacing air handler in attic, coils, etc. No attic fan in the attic. They said “it was too hot in the attic to light the torch so for now they are getting us 2 window units.” What the heck would that mean??

    1. Hi! Thanks so much for your question. More than likely the problem is that it is too hot to work in the attic. Sometimes the temperature can be over 130 degrees without an attic fan. They are probably concerned over their health and would rather come back in the morning when the attic is cooler. I hope you have a great day and weekend! Steve

  45. Replace expansion valve on evaporator vacumn unit started charging unit had 150 on suction line turned unit on pressure dropped to 20 suction line frosted up unit shut off unit won’t run long enough to charge 410-a system

    1. Hi Mr. Vuorela!
      You will need to wire past the low pressure safety switch in order to charge the unit. You can hook the low pressure switch back up after you get the system fully charged. I hope this solves your problem.

  46. Hello,

    My home was hit by lightning last week. Thankfully, no fire. However, my HVAC control board was fried and we lost our AC. I was told that the control board just needed to be replaced. However, I have concerns over all of the components of the entire HVAC unit. I believe that the other HVAC components can’t fully be tested/measured until the control board is once again functional. Therefore, what else could have been compromised on the unit and could there be other integrity issues to consider on my 11 year old HVAC unit. Repair? Replace?

    Please let me know what you advise as I desire to get my AC back on soon. Thank you.

    1. Hi Will!
      Sorry to hear that your home was hit by lighting! A lightning strike can mess up many components both in your home, furnace and AC unit. I have seen compressor blown up when lighting strikes. I hope that all you need is a control board and this is a good possibility, but lighting could damage anything that is high or low voltage. On the low voltage side the control board, thermostat, transformer and contactor. On the high voltage side the compressor and fan motor. I hope that it is only the control board. Thanks so much for asking this question. Steve

  47. I read through the problems and didn’t see anything resembling mine. So here we go. I have a Day&Night 3 ton AC in a new home and this is its first season. It appeared to run fine last fall, but it was never really used. With summer here, I am experiencing a problem with the unit restarting after a cycle. The stat has a 5 minute short cycle protection. I first noticed the problem on a hot day when it kicked on after a 15 minute rest from the last cycle. The fan kicks on and the conpressor locks and shows locked amperage. If it is allowed to sit for 30+ minutes it seems to start fine, or if it is cooled with water before starting it will start.
    My guess is that the coolant is not equalizing quickly enough, and I don’t have gauges to confirm this. Could this be because my evap coil is on the second story and the condenser is at ground level?

    Or would you suspect something else? It performs fine when it runs, temp differential is 17 degrees f.

    1. Hi Cameron! Thanks for asking this great question! Since the unit is having trouble starting I would suggest that you make sure that the run capacitor for the compressor is in good shape and not weak. If the capacitor is in good shape I would suggest that you try installing a hard start booster like the SPP6 that we sell on the following page: https://arnoldservice.com/product/supco-spp6-compressor-hard-start-booster-capacitor/ I would recommend turning off the power after the unit runs for a while and see if the compressor is hot on top. If the compressor is hot on the top then you might be low on refrigerant charge. Yes, you are correct, in order to get the cool refrigerant gas coming back to the compressor from and evaporator on the 2nd floor, they might of had to over-charge the unit thus making the compressor have a hard time starting. I would highly recommend trying a hard start booster. I hope you get find and fix the problem soon. Steve

  48. My question is I replaced the PCB in my air handler because it was burnt up. now the bower motor runs on heat but not ac setting?

    1. Hi Byron! I would suggest that you check to make sure the thermostat is sending 24 to 28 volts AC to the G (green) thermostat wire when the thermostat is calling for cooling. You should have 24 volts AC between the G and C (com) terminals on the control board when your thermostat is calling for cooling. This is what causes the fan relay on the control board to close and runs the fan in the cooling mode. If you aren’t getting 24 volts between G and C then you probably have a thermostat or a thermostat wire problem. The only other reason that I can see that would cause this problem would be if the control board is wired wrong, or if you have a faulty control board. I hope you can easily find and fix the problem. Steve

  49. I got a Carrier HVAC outside unit that keep burning the contactor It was working fine then, start switching off and on. I disconnect the power and saw the burned and stuck down contactor. I replace and I notice it was doing the same running even with the thermostat off the unit was running and stopping and making a buzzing noise and burning the contactor and turn in off and on by itself. I removed the connection from the board and stop. Or if I remove he thermostat the unit stop. What can I do to ensure the unit stop burning the contactors. I check 220 coming in and coming out ok, I check 24 V from left to right of contactor ok. I notice in another unit somebody put an extra switch with a 2nd capacitador. What would be the solution of this problem.

    1. Hi Carlos! A problem that can cause contactors to fail quick is if the contactor is not getting enough low voltage to the coil. Please make sure the contactor is getting at least 24 volts AC to the coil. If the contactor is not getting the needed 24 volts then this can cause the contacts to chatter and burn up quick! I have seen weak transformers, weak batteries in a thermostat and shorted thermostat wires cause this problem. If you hear your contactor chatter then please find out what is causing the low voltage problem soon, because this chatter will cause a contactor to fail soon. We discuss this problem on the following page: https://arnoldservice.com/problem-air-conditioning-outdoor-condensing-unit-or-heat-pump-unit-will-not-shut-off-it-continues-to-run-no-matter-what-you-do/ Another cause of quick contactor failure would be if your unit is low on charge and the low pressure safety switch is shutting the unit off an on. If your unit is low on charge and if you have a low pressure safety switch then every time the unit comes on then the pressure will go too low and the safety switch will shut the unit off. I would suggest making sure your refrigerant charge is right. I hope you can easily find and fix the problem.

  50. We’ve been having issues with our unit. We can’t go below 78 or it seems to blow not hot air but not cold either. The unit outside isn’t frozen up from the looks of it. We were told our defrost board was blinking, but was told we had a bad thermostat. We’ve changed that out, but still having the same issues. We turn the unit off for HOURS and then it will work fine for a day or two and do it again. We’re not sure if this is because of the defrost board or if made our fan is over heating or possibly going out.

    1. Hi Ms. Marino! Thanks you so much for asking this question! This sounds like your air conditioning/heat pump system is low on refrigerant charge. Whenever you see the unit on the outside frozen up it is a sure sign of the system being low on charge or having poor air flow with a possible dirty filter, dirty/stopped up evaporator coil or a slow blower motor (might need a new capacitor). Most of the time the problem of freeze ups are caused by being low on refrigerant charge. I would suggest that you have your heat pump unit tested to make sure it has the right amount of refrigerant. I hope you have a nice day! Steve

  51. I have a 2-story home with 3 and 2 tons A/C units. Recently these units are replaced along with both furnaces. Now we feel poor/weak airflow from most of the vents. With old units, it was comfortable with 78F setting in summer, but now it’s required 74F. Also, when 6+ people in room, unit seems to run continuously. Overall, very unpredictable (not cooling well when outside temp goes up). The coil got frozen earlier and installer replaced TXV on both but didn’t help. The airflow is weak/restricted, hot in bedrooms and fine in some area. What could be the issue? What should I ask the installer to check?
    Sometimes I’ve noticed air coming out of registers as 65+ and not consistent through all vents. Thank you. – Sam

    1. Hi Sam! Sorry you are having air conditioning problems after getting two new systems! This most certainly sounds like an air flow problem or a problem where the company did not install a large enough units. Did the company do a heat gain, heat loss calculation before installing the new systems? It is code here in Louisville, KY. to have a heat gain and heat loss calculation submitted to the housing department before they will issue a permit. This insures you get the right sized equipment installed. This could also be caused by a filter that is too restrictive. I would make sure you have a filter installed that is not too restrictive. Some of the filters will cut your air flow down lots. The temperature of the air coming out of the registers should be at least a 15 to 20 degree difference from your indoor ambient temperature. I would also ask the company if they can turn the blower speed up because you are not getting adequate air flow. I hope you can get this company to take care of your problems. Thanks so much for asking the question. Steve

  52. I recently had my HVAC unit replaced. The old one was a 2 zone system with upstairs and downstairs being controlled individually. When my HVAC professional replaced the old one he said they had to bypass the zone system as the pressure was too high due to increase in airflow and was causing pressure build up. After the first 3-4 weeks we began having problems with the outside fan and unit shutting down. My HVAC guy said the head pressure was too high so it was shutting itself down until the pressure stabilized then came back on. Looking at your site I am wondering if it may be the capacitor
    or some other cause than just the ducts won’t handle the excess flow of air from our new super unit. I have a two story 2450 SQFT home and this only happens when it gets really hot outside. Any suggestions? They were out last week early in the AM to reroute ducts and airflow , but it was not yet hot enough for the pressure to increase so they said they will come back when it is hotter. Of course it is hot today (Sunday)!!
    Thanks for your blog and all the helpful information! Jan

    1. Hi Jan! Sorry you are having this problem on this hot day! This sounds like the furnace blower might be too strong for the air conditioner that was installed. If the AC is too small for the furnace blower then the installers might have had to over-charge the unit in order to get cool gas going back to the compressor to keep the compressor running cool. Your problem sounds like you have an air conditioner that is either over-charged or you have a restriction in the refrigeration system that is causing it to go off on high head pressure. I would suggest that you call your HVAC contractor back out and have them find out where the problem is and fix it. Your new unit should be under warranty for both parts and labor. I hope you can get it fixed soon! Thanks so much for the great question! Steve

  53. When turning on A/C after it’s been off for an hour or so it works fine, all pressures and temps normal at compressor and compressor fan running good, (with cool air coming through the vents). All Good. After about 10-15 minutes, (well before the thermostat reaches the target temp setting), the compressor fan turns off… the compressor stays running… the pressure builds to about 650psi in about 30 seconds… and then the compressor turns off. The pressure slowly backs down below 300 in about a min. If I leave the system on, in about three or four minutes the compressor starts back up, but the fan stays off. Pressure builds back up to about 650psi again and compressor turns off. If I leave the system on it just continues this cycle. If I turn off the system, (off at the thermostat), for a few hours it runs fine again for 10-15 min then starts the whole cycle again. (Carrier 25HBA / R-410A) …Greatly appreciate your help! Thanks, Joe

    1. Hi Joe! This sounds like you either have a fan motor problem or possibly a fan capacitor problem. This sounds like the fan is cutting off during the cooling cycle which causes the unit to run high head pressure. This is very hard on your compressor and could damage the compressor if you let this continue. I would suggest that you see if the fan motor is getting 220 to 245 volts during the time it cuts out. If the fan is getting the 220 volts and cutting off then you either need a new fan motor or capacitor. I would suggest you take the capacitor to have it checked to make sure it is not weak. A weak capacitor will also cause a fan motor to stop. Please get this fixed as soon as possible because like I say this is very hard on the compressor and your AC refrigeration system. Thanks for asking the question! Steve

      1. Thanks Steve!!! Appreciate the quick response too! Taking the fan motor option I ran water from a hose over the top of the unit onto the motor to see if that kept it from overheating and tripping it’s over-temp circuit. So far it hasn’t quit, (about an hour now and still running…) So guess I’ll swap out the motor & capacitor… Again, thanks for the help!!!

      2. Thanks Joe! Glad to hear that you found the problem in either the motor or the capacitor. If the fan motor blade is a little hard to turn and does not spin freely then you probably have a tight bearing in the motor and you will need a new motor. Thanks so much for the question and solution to the problem. Hope you have a nice weekend! Steve

  54. Steve
    I have a problem for had the system charge last night high side about 240 and low was about 55 system ran great last night, came home today house was hot 80 degree went out to the system fan is blowing feels lick cool air put gauges on low side is at 140 and high side is at 150 cant hear the compressor turning on HELP

    1. Hi Mr. Arnold! Thanks so much for asking this great question. With the pressure a 240 and 55 psi and with using R22 as the refrigerant this shows that the system is low on charge. Low side pressure should be above freezing and if using R22 should be 58 psi or more. More than likely over time the evaporator coil will freeze like a block of ice, impede the air flow and could slug out the compressor. Slugging the compressor out with liquid refrigerant is not what you ever want because the compressor is made to pump a gas and not a liquid. The liquid inside the compressor can cause the valves inside the compressor to become bent and not sell anymore. I hope the compressor was not slugged out and hope it did not bend one of the valves. With the pressures 140 and 150 this shows that the compressor is not doing its job and not making the difference in the high and low side. If the compressor is running then this is a sure sign the valves on the compressor have blown or the compressor high pressure relief valve has not reset. I would try turning off the compressor and let it set for a couple of hours and see if it will reset the valves or the pressure relief valve. If it does start making the difference in the high and low side again then I would recommend having the refrigerant charge checked out. I hope the compressor resets and starts working right again. If the compressor does not start working right again then you will need a new compressor. I hope it starts working right again. Thanks again for your question. Steve

  55. My central ac unit blower fan is making a rumbling noise. It’s blowing fine, just louder than it was last year. Could the fan cage just be dirty?

    1. Hi Keith! Yes, The blower wheel could be dirty or off balance and cause a rumbling sound. I would like to suggest that you turn the power off to the unit and use a mirror and flashlight to inspect the blower wheel to make sure it is clean. I have found pieces of paper and lint in blower wheels that cause them to be off balance and rattle. Rumbling noises can also be caused by loose motor bearings (motor getting ready to go out), something loose in the duct work like a damper or metal, or refrigerant flow can sometimes rubble when it goes through the refrigerant lines. Refrigerant flow usually does not make a loud rumbling sound. I hope that I have given you some insight on what to look for. I hope you can easily find where the rumble is coming from. I hope you have a blessed day! Steve Arnold

  56. On a RUDD heatpump with the entire unit on the outside. The unit starts but the low side pulls down to zero and cuts the unit off a tech was by but he was puzzled by it too. We cleaned the evaperator on the inside of the outside unit it was dirty but that was not the problem it is still pulling the low side down to zero and cutting the unit off…

    1. Hi Mr. Brown! When the low side pulls down to zero when the unit turns on this is a sure sign of being low on refrigerant charge or having a restriction in the system. Most of the time it is caused by being low on charge. I have also seen stopped up metering devices like restrictor pins or thermostatic expansion valves that will cause this to happen. If the unit is not low on charge then you probably have a stopped up metering device. Here is a good YouTube video that discusses metering devices. I hope you have a blessed day! Steve Arnold

  57. I have a 93% efficient furnace but when changing a breaker the return wire became caught against a 20amp hot line. the furnace made a humming sound then a pop. as a result the furnace does not work and the central air is also affected. What are likely solutions to get the system up and running?

    1. Hi Jay!
      Sorry to hear this happened. Hopefully the fuse is blown on your control board and it did not burn the control board up. We discuss the fuse problem on the following page: https://arnoldserv.wpengine.com/problem-furnace-air-conditioner-heat-pump-will-not-come-on/ If a hot wire touched the furnace ground wire then it could have fried the control board circuit. I would suggest testing with a meter and go through the AC troubleshooting flow chart that we have on the following page: https://arnoldserv.wpengine.com/air-conditioner-troubleshooting-flow-chart/ I would start with setting the AC to cool and turn the thermostat down so it should be cooling. Test with a volt meter set to volts AC. between terminals R and C (com) and between terminals Y and C and between terminals G and C. All of these should give you a reading of 24 to 28 volts AC. If not then the transformer or thermostat might be a problem. Best of luck in finding and fixing the problem. Steve Arnold

  58. I have a issue with the a ac unit the unit starts the motor doesn’t I change the motor but it still doesn’t come on

    1. Hi Olivia!
      Sorry to hear that you are having AC problems during this hot weather. Please make sure the motor is wired properly as shown on the motor label. Please make sure that you are getting 210 to 245 volts to the motor when the contactor closes and when the unit is calling for cooling. Please make sure the motor capacitor is the right size and is in good shape. You might want to make sure the capacitor is in good shape by having it tested at a local appliance parts store. We have a questions and answers troubleshooting page with lots of YouTube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ I hope this will help you to easily find and fix the problem. Steve

  59. My air unit is only 5 years old. The outside fan works great. I can hear The compressor running one minute and then it just shuts off. It kicks on and off. (Possibly overheating? NOT sure) Not a constant on and off. It will sometimes take 10 minutes or 30 mins or an hour to kick back on. Stay on for 30 minutes or so and kick back off.(without cooling the house) outside unit fan will be running by itself without the compressor running. I can turn the unit off for a few seconds and then back on and sometimes the compressor will kick on right away and sometimes it wont. It makes a loud hissing/blowing sound sometimes. The unit will quick/short start (not sure if that is what its called) the outside unit will be running and it kicks off for like a second or 2 and comes right back on. It doesn’t do it all the time though. works perfect during the night or on a cloudy or cool day. Only messes up during the day when its hot and sunny outside. Doesn’t freeze inside or out. New clean filters. Inside and outside ciols aren’t clogged. What is going on?

    1. Hi Tina! This sounds like your compressor is probably over-heating and going off on internal thermal over-load protection. Compressors that over-heat can be caused by dirty outside coils, slow fan motors, (might need a new capacitor) could be low on refrigerant charge. I would suggest turning the power off to the unit when it shuts down and lightly touch the top of the compressor. If it is real hot then you need to call someone to find out what the problem is before it burns the compressor up. We have a troubleshooting question and answer page which has many questions with YouTube troubleshooting videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ I hope you can find and fix this problem easily. Steve Arnold

      1. Thanks Steve. I forgot to add that the high pressure side is getting up over 630. Is that normal?

      2. Hi Tina!
        630 PSI is way too high! I am surprised your unit has not blown up! High head pressure can be caused by dirty outside coils, slow fan motors, (might need a new capacitor) or a restriction in the refrigeration system. I would suggest that you get this checked out with a professional before it permanently damages your unit. Steve

  60. what causes the compressor terminals to burn

    1. Hi! Thanks for the great question! Most of the time compressor terminals burn because of a loose connection caused by the vibration from the compressor, moisture from rain or from a sweating compressor. Most of the time it is from a loose connection. When there is a loose connection the terminal arcs and causes lots of heat, thus melting the terminal and connection over time. God bless you and your family today and always. Steve

  61. i live in a mobile home and have the right size ac for the footage of the home. The AC is rather new. I had the AC serviced, coils cleaned and etc. The duct work inspected by two companies which both said it was fine. Then I had the ceiling filters cleaned out. My problem is that I set my AC on 78 degrees during the day (I live in Florida) and the unit runs all day long I mean all day and at night I set it to 76 and it takes 2-3. hours to get to 76 degrees. Out of 10 vents total in my house only 3 blow out cool air. Actually the whole house stays warm all the time and I sweat most of the time. Any suggestions what to do or who to call. I keep my windows closed all the time now and I don’t really like living in the dark. Thank you in advance for any suggestion.

    1. Hi!
      I am terribly sorry to hear that your AC is not working right. Something has to be messed up for the unit not to cool properly and for only 3 of the vents to be blowing cold air. Some of your duct work must be disconnected or having a heat gain from the roof or from somewhere. I would like to suggest that you ask other friends to see who they recommend, or call the Better Business Bureau and ask them who they would recommend. You might look at Angie’s list in the reviews and see who other people liked in your area that do AC work. It sounds like the company that you are having is not doing a good job. Sorry for your trouble! I hope you have a blessed Memorial Day Weekend!
      Steve Arnold, https://arnoldservice.com

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