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.

Please read the following:

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.

One thought on “Popular HVAC Questions & Answers

  1. 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.

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