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Top 12 Problems/Mistakes when Installing or Replacing a Thermostat! HVAC Tips!

We have had many questions and problems about thermostats and about thermostat installations. I found a very good video on the ACservicetech youtube channel. Please click here if you are interested in seeing some of the many outstanding HVAC service and troubleshooting videos.   Below we have an excellent Youtube video that I copied from the ACservicetech channel which shows 12 problems, mistakes that we can make when installing or replacing a thermostat. I hope this helps you out. If you have any questions please email me, Steve Arnold anytime. Our email address is: support@arnoldservice.com. We would love to help you out and earn your business!

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My furnace / air conditioner cooling coil under my house is causing water to puddle up on the ground. What will cause this to happen and what do I need to do to fix it?

troubleshooting air conditioners and heat pumps

Water under the cooling coil can be caused by several things. (1) Most of the time it is caused by a stopped up condensate drain line and you should be able to blow compressed air through the line or take a wet vac and suck on the end of the condensate line to clear the clog. In severe cases sometimes the condensate line has to be cut with a saw or PVC cutter to remove the clog. I have also had to remove the evaporator coil covers to get to the coil drain pan and drain pan opening in order to clean the coil drain pan and condensate drain opening with a wet vac to get the coil drain unstopped and clean the coil drain pan while I have the evaporator coil open. I would suggest testing the coil drain pan with water by pouring water into the coil drain pan with a cup or bottle to make sure the drain is open before closing the evaporator coil back up.  (2) Sometimes coil drain pans develop holes and you would need to repair the leak in the pan by using epoxy of silicone caulk. I would try to make sure the condensate drain line is open before checking to see if the evaporator coil drain pan is leaking. If the condensate drain line is open and you are not getting any water or not much water out of the condensate drain then more than likely you have a hole in the condensate drain pan. I have tried to repair the pans before with epoxy and silicone, but most of the time this fix will only last one or two years. If you have a leak in the evaporator coil drain pan I would recommend replacing the entire coil. Repairing the drain pan can be time consuming and like I said usually does not last long because the coil pan has probably deteriorated in other places. Most of the time the entire evaporator coil has to be removed to do the repair. I some cases I had my sheet metal man make a new coil pans, but removing the old coil with all the movement, screwing on a new coil pan and heating the refrigeration lines to reinstall the coil after the new pan has been installed can cause refrigerant leaks. In my opinion after many years it is best to get a whole new evaporator coil and be done with it. (3) water on the floor around an evaporator coil or furnace can also be caused by a system being low on refrigeration charge and freezing up because of being low on charge or having poor air flow. Most of the time if a coil freezes up it is caused by a low charge, but I have seen cases where a dirty filter, dirty evaporator coil, or slow blower motor (might need a new motor capacitor) have caused evaporator coils to freeze up melt and cause water on the floor. If your coil is freezing up I would suggest checking anything and everything that could cause poor air flow across the coil and if everything is clean call a service tech to check the refrigeration charge in your air conditioning or heat pump system. I hope I have given you some things to look for if you find water on the floor around the furnace or under the air conditioner air handler. If you have any other questions please ask anytime. Our email address is: support@arnoldservice.com

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Do not test a pressure switch by sucking on the pressure switch tubing.

I wanted to post this because many people are telling me that they are sucking on the pressure switch tubing to test pressure switch operation. I have heard from other forums that you should not suck on the pressure switch to test it because this can damage the diaphragm inside the pressure switch. It would be best to use a manometer or test with a volt meter like we advise on the following page: https://arnoldservice.com/how-to-test-and-troubleshoot-gas-furnace-pressure-switches/ I wanted to pass this along so others will not damage pressure switches. Please feel free to comment below.

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Problem: Why do the gas burners on my furnace shut off after being on for only a minute or two?

QuestionHi, I have a BDP/Carrier furnace from 1987. The burners will light and run for about a minute or two, but within a minute after the blower turns on the burners and pilot go out. If I remove the cover to the blowers the burners will stay on and heat the house. I checked to make sure the air intake vents in the house are not covered. Any suggestions?

AnswerHi Darren! Great question! This sounds like the furnace is probably over-heating and going off on limit. I would suggest that the next time the furnace gas goes off prematurely that you check the limit with a volt meter to see if the limit is the problem. You might need a new limit or more than likely the limit is doing its job by cutting off the furnace to keep the furnace from getting too hot. Over-heating of the furnace can be caused by as you have already checked some of the registers being blocked or turned off. Over heating of the furnace can also be caused by a dirty filter, dirty blower wheel, slow blower motor, (might need a new capacitor) stopped up or blocked air conditioner evaporator coil or the gas valve gas pressure being set too high. I would suggest checking the easy causes first like the filter, dirty blower wheel or have the capacitor on the blower motor checked. Best of luck in finding and fixing this problem.

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Problem: Why does my air conditioner fan motor keep burning up?

troubleshooting air conditioners and heat pumps

Question: In May I started to have some problems with my outside ac unit. My fan stopped running but I could get it back running by spinning the blade when it hmmmmmed. Blade was easy to spin Called an AC Company to see what was wrong They said the fan motor was bad and put in a new fan motor and oval capacitor.
But didn’t replace the dual capacitor said it didn’t need to be replace it was good. Ran good and cooled down the house good for about a mouth or so but started having the same problems. My fan stop running I could get it back running by spinning the blade when it hmmmmmed. Blade was easy to spin, but motor was hot to the touch
Ac company came out again said it was a bad new motor. Company put in a new fan motor and oval capacitor but didn’t replace the dual capacitor said it didn’t need to be replaced that the capacitor was good. Ran good and cooled down the house good for about a mouth or so but started having the same problems. My fan stopped running but it’s hard to spin now and takes a couple of tries to spin when it hmmmmms. The motor was hot to the touch. Now the fan motor won’t start to spin by me spinning it at all. It is too hard to spin. Note: The motor is still hot to the touch. What could be possible wrong with my unit? Why does my fan motor keep burning up?

Answer: Hi! I am so sorry to hear that you are having all these problems with your fan motor. There are several things that can cause a fan motor to go out prematurely. I will list some of them below then you can assess whether any of these might be causing your fan motor to go out so often.
1. Installing a universal fan motor that is not matched correctly with the right RPM or horsepower to power the fan blade. Motor not matched to the diameter and pitch of the fan blade. Motors should be matched (RPM, Horsepower, Amps) with the fan blades or it will over-load the motor and the motor will fail soon.
2. Having a fan blade that is off-balance and causes vibration to the motor and unit. A new balanced blade would be best.
3. Installing a fan motor and capacitor where the capacitor does not match the specs on the label of the fan motor. The fan motor capacitor should match the specifications on the motor label.
4. Installing a fan motor where lots of moisture is present like from a leaking gutter or down spout. Water pours on to fan motor when it rains or when snow melts.
5. Not having the rain shield installed (when required) or leaving drain plugs open where water and moisture can get into the motor. Some motors have rain shields to prevent water from getting into the motor. Many universal motors do not have rain shields, but have drain plugs that can be opened or closed depending on how the motor is installed, horizontal, vertical, shaft up or shaft down.
6. Improper wiring. Where the motor is not wired according to the label on the motor.
7. Improper rotation of the fan blade. With the fan blade spinning in the wrong direction the motor will not load and it will burn up over time.
7. Grass, weeds, plants or children that stick into the fan blade path and stop or impede the fan motor when it is running.
More than likely the HVAC company you had installed a universal fan motor. Many of these motors use an individual capacitor and this is why they did not hook into your existing dual capacitor. They probably are using the dual capacitor for the compressor only and the fan motor they installed has a separate single capacitor. I am just guessing. I am thinking that probably number 1 is probably the problem. That is why we mostly sell OEM fan motors so they will be matched with the fan blade and the customer has an easy time with the installation. If you would send your unit’s model number I will try to find out which OEM motor fits your unit. Our support email address is: support@arnoldservice.com. We will be glad to try and help you out!  Steve Arnold

Please comment below if you would like to add to this post or email us at: support@arnoldservice.com

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Problem: Furnace blink code shows I have a pressure switch problem. Replaced pressure switch. Still have a problem?

Problem: Hello, love the website and help that it offers. But I seem to be out of options with my furnace here. I have a Carrier HE furnace that is not even 3 years old yet. We have had repeated issues with the furnace running for 2-3 minutes, stopping, recycling and coming back on until desired temp is reach. Sometimes this will occur 3-4 times depending on reaching desired temp in the home. When I called a technician he came out and charged 170$ just to tell me my pressure switch was broken. And offered to replace it for another 150$(!). I ordered one myself and replaced it last weekend. Took me 5 minutes and switch was 60$. But, I’m still having the same symptoms. Sometimes the furnace will not even come on and we awake to a cold house. Other times it works just fine…??… it’s “buggy” as I describe it. I am getting a 3 to 1 LED code indicating pressure problems. But I have cleaned the water trap multiple times and there seems to be no issue. No water lines to or from are blocked. Exhaust is not blocked leading outside. Nor is intake. And again the pressure switch is brand new (supposedly). And I have also cleaned the flame sensor with newspaper (no steel wool). I don’t believe that is the problem. Seems clean. No residue on it. So, if you can offer any help please do! Cleveland is about to have sub zero Temps coming up this weekend! Chris

Answer:  Hi! I am terribly sorry that you have encountered all these problems with your furnace. We have a furnace troubleshooting flow chart that I hope will help you out on the following page: Please click here if you would like to see our Gas Furnace Troubleshooting Flow Chart. I would start with making sure the thermostat is providing 24 volts between W and C terminals on the control board when the furnace cuts off. If you are getting a constant 24 to 28 volts AC to the furnace all the time between W and C when the furnace cuts off then this would eliminate the thermostat from being the problem. If the control board is correct in saying and showing that the pressure switch is the problem… then I would suggest looking at the things like you have already have, like the condensate trap and drain lines from the secondary heat exchanger. Please make sure the furnace is tilting forward slightly so the water drains out the front of the furnace. The installation instructions on these high efficiency furnace tells how many feet of vent pipe are allowed for venting. If the allowed vent feet are exceeded then you will have trouble with the pressure switch not staying closed. The 90 degree turns in the venting sometimes are calculated as 5 feet of piping. If you have exceeded the number of turns the furnace will not run right and the pressure switch will not work or stay closed. I remember one furnace I installed where I tried to use 2″ PVC for the venting and ended up having trouble with the pressure switch going off like your furnace is doing. I ended up having to tear the 2″ pipe out and install 3″ PVC vent. The venting is critical for these high efficiency furnaces to run right, to say the least! Some other things that cause furnace pressure switch problems are: (1) A restricted vent pipe (2) Too long of vent piping and too many turns which exceeds manufacturer’s recommendations (3) a stopped up condensate drain line if you have a high efficiency condensing furnace. (4) a dirty or stopped up draft inducer. The hole where the pressure switch attaches to the draft inducer could be stopped up with water, slug or dirty. (5) a slow draft inducer that might need a new capacitor or has slowed down. (6) someone has sucked on the pressure switch with their mouth or forgot to unhook the pressure switch from the furnace before using a vac on the furnace. Sucking on the pressure switch or leaving a pressure switch attached to furnace when vacuuming out the condensate line will ruin the diaphragm on the pressure switch. I hope you can find and fix the problem. If you need parts please send me your furnace’s product number. Please email us anytime if you have a question. Our email address is: support@arnoldservice.com. If you think you have a bad pressure switch please click here to see the furnace pressure switches we sell. I hope you have a blessed day.  Steve Arnold, https://arnoldservice.com

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Problem: Burners ignite the gas valve cuts off after only a second because the pressure switch is opening for a split second.

Problem: Can a draft inducer motor somehow get “weak” before it seizes up or shows some type of problem? My furnace code is telling me pressure switch/vent problem but I have checked both and they function fine. The problem is when the burners ignite the gas valve cuts off after only a second or two because the pressure switch much be opening for a split second (if I bypass the switch the burners stay ignited and everything works). With no vent problems and pressure switch working like it should I am down to thinking that either the inducer motor is not keeping up when the burner ignites and gives a little burst of pressure, or maybe the gas volume is set a little too high so that the burst of ignition is causing a pressure pulse that opens the switch. I’m not sure which one would be more common after running fine for 10 years. If I run the furnace for a few minutes with pressure switch bypassed, and then shut down, hook switch back up and restart, the system will ignite and run as it should, but later after being off for a while it will not stay lit and does the same thing and gives same code.  This leads me to believe that when vent and system is hot it can draft better and switch will not open when burner first ignites so whatever the problem is, it is just barely giving enough pressure change to open the switch when ignited and system is cold. Inducer or gas volume or have you seen something in this situation that could be the problem? Thanks.

Answer: Excellent question! I have seen this problem happen before when I was doing service work. Most of the time it was caused by the pressure switch itself being the problem. The diaphragm inside the pressure switch gets tight over time or the diaphragm develops a small leak and will not sense the right pressure. Please click here if you would like to see the pressures switches that we sell.  Please email us anytime with your furnace’s model number if you would like for us to look up part numbers for you. Our email address is: support@arnoldservice.com We would Love to Help You Out and Have Your Business!

The second most common cause is the pressure switch tubing (line) being slightly obstructed with water or debris. If your Lennox furnace is a condensing furnace that produces water when it runs, then please make sure the water drain line on the furnace is draining well. Please make sure the pressure switch tubing where it attaches into the draft inducer is not obstructed with water, or the hole where the pressure switch tubing attaches to the draft inducer is not obstructed. If you are having a slight delayed ignition when the furnace first starts up then you might want to clean the burners with compressed air. Clean the pilot or furnace lighting mechanism to make sure the furnace lights smoothly. Too much gas pressure or too little gas pressure can cause a furnace to have delayed ignition. You can adjust the gas pressure if you think you might be getting too much or too little gas pressure.  I show how you can do this on the following page: Please click here if you would like to see our Gas Furnace Troubleshooting Simplified Page. Please be careful when trying to adjust gas valve gas pressure. This can be dangerous when working with natural gas. A draft inducer’s bearings can get tight, or the inducer blower wheel can get dirty which could slow it down. Please make sure that the draft inducer wheel turns freely. A good test would be to watch to see how long the draft inducer wheel spins after the draft inducer goes off. The wheel should spin from 3 to 5 seconds after the power goes off to the draft inducer. If the draft inducer does not spin very long (only a second or two) then the bearings on the draft inducer might be tight and you will need to purchase a new draft inducer or a new inducer motor.  If your draft inducer has a run capacitor you might want to check the capacitor to make sure it is reading in the right specs and not weak.  A weak capacitor will cause the draft inducer to run slow. You said, the vent is not obstructed so this isn’t the problem. I would also suggest to look at the things on the furnace like the condensate trap and drain lines from the secondary heat exchanger. Please make sure the furnace is tilting forward slightly so the water drains out the front of the furnace. The installation instructions on these high efficiency furnace tells how many feet of vent pipe are allowed for venting. If the allowed vent feet are exceeded then you will have trouble with the pressure switch not staying closed. The 90 degree turns in the plastic PVC venting sometimes are calculated as 5 feet of piping. If you have exceeded the number of turns the furnace will not run right and the pressure switch will not work or stay closed. I remember one furnace I installed where I tried to use 2″ PVC for the venting and ended up having trouble with the pressure switch going off like your furnace is doing. I ended up having to tear the 2″ pipe out and install 3″ PVC vent. The venting is critical for these high efficiency furnaces to run right, to say the least!  I hope that I given you some insight into what might be the problem. I am sorry we do not sell very many Lennox parts but I will be glad to try and help you out anyway I can. Steve Arnold, https://arnoldservice.com

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Problem: Outdoor heat pump unit makes a loud sound in the winter? What is this noise?

AC parts

Question: Hi, thank you.  We have a standard all-electric attic blower with outdoor condenser Carrier AC/heat unit.  In the winter, in the middle of the night, the unit outside will make a loud decompression/discharge sound, almost like firing a torpedo.  Not a squeak or rattle or gurgle, but a one-time bwwwuuuusshhhh.  Once or twice a night, when it’s pretty cold out.  loud enough to wake us up. Chris, Buckeye Arizona.

Answer: Thanks so much for your interest in our website and the opportunity to do business with you! From what you describe this sounds like you probably have a heat pump unit and the noise that you are hearing is probably the heat pump going into defrost mode. When a heat pump goes into defrost the reversing valve will shift into cooling mode so the outdoor unit will be defrosted. During this defrost time the heat pump defrost control should turn your indoor electric heaters on so you do not get air conditioned cold air coming out of the registers. If it is cold enough outside you will probably see smoke (moisture) raising above the outdoor unit. I have had heat pump customers call me saying it looks like their outdoor unit is on fire when actually this is normal. Yes, going into defrost mode on some heat pumps can be noisy when the reversing valve shifts the outdoor fan turns off and your indoor electric heaters are energized. I hope this is the problem because this is normal from a heat pump. If it becomes too noisy you might want to call a service tech to come and make sure the operating pressures and refrigerant levels are right. Below we have a real good YouTube video made by Air Comfort Heating and AC which explains how a heat pump system defrosts and what to expect. I hope that you have a blessed day. Steve

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Problem: No gas.. bad control board? Frazier Johnson heater

Problem: I have tried about everything. I have no gas. I unplugged the gas valve connector from the control board and plugged it back in.  The burners started working for 3-4seconds, then again after that back to nothing. The draft inducer comes on, the igniter comes on,  But no gas.. no valve noise no call to open gas valve. No volts at valve.. can u help its 25degrees n kansas. Thanks.

AnswerSorry to hear that you are having furnace trouble so early on a Sunday morning!  Yes, this does sound like a possible bad control board. I would suggest using a volt meter to make sure that all your safety controls are closed like the pressure switch, limit switch, rollout switches (if equipped). Please check all your wire connections and make sure the ground wire coming off the transformer and other wires are good and tight. If all your safety controls are closing and still no voltage to the gas valve then I would say that you probably have a bad gas valve relay on the control board. You might try lightly tapping on this gas valve control board relay with your finger to see if you can get the relay’s contacts to close and start working. We have a page that I hope will help you out. Here is the link: Please click here if you would like to see our Gas & Electric Furnace Troubleshooting Simplified Page. I believe that Frazier Johnson is similar to a York furnace. I could be wrong, but if you want me to look up parts I will be glad to look up parts if my York program can find your model number. Please email us anytime if you have questions. Our email address is: support@arnoldservice.com. Hope you have a blessed day! Steve

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Question: If I slow down the fan speed on my inside air handler will it effect the outside unit?

Happy AC

Question: If I slow down the fan speed on my inside air handler will it effect the outside unit? I have a amana 14 seer heat pump.

Answer:  I would not be recommended slowing down the fan speed on a heat pump unit because the indoor coil becomes the condensing unit in the winter and this might cause high head pressure thus damaging your heat pump unit. If you have gauges you could try to lower the speed and see if the head pressure goes up too high or not. There should be a graph type chart that is located inside the control box of your heat pump outdoor unit. On the paper it should show a graph with recommended pressures, both high and low pressures for different temperatures. If you can lower the fan speed and stay in the manufacturer’s recommendations then you should be OK.