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Problem: Air conditioner outdoor unit will not come on. Nothing happens.

Happy AC

Near the bottom of this page we have a real good Youtube Video made by Acservicetech that shows how to troubleshoot an air conditioner if the air conditioner outside unit is not turning on.  Many thanks to the AC Service Tech Channel!

Problem: This problem is probably the second most common problem that I see every summer in our HVAC business. The problem most of the time is a bad run capacitor. The Air conditioner outdoor unit will not come on. Either the outdoor fan does not run, the compressor does not run, or both the fan and the compressor do not run. Sometimes it can be a contactor problem. If you see that the contacts on the contactor or burnt or not engaged (energized) then you might either have a contactor problem or a low voltage problem (not getting 24 volts AC to the contactor). We sell contactors on the following page: Please click here if you would like to see the contactors we sell.

Solution: You probably need a new run capacitor or contactor. We have a real good air conditioning troubleshooting YouTube video near the bottom of this page that ucberk599 produced. This video discusses and shows how to install a new capacitor. Please click here if you would like to see the capacitors we sell.

1. I would first recommend turning your thermostat to Off and then reset your air conditioner’s circuit breaker. Most of the time home air conditioners run on a 30 or 40 amp double pole breaker. Always were shoes and do not touch any metal part of the breaker box when resetting a circuit breaker. Reset the circuit breaker with two fingers on the breaker handle only.  Below grayfurnaceman made a video on how to check to see if there is power coming from the disconnect box to your air conditioner’s contactor. I have seen people have one hand leaning on the breaker box and the other hand resetting the breaker!Do not do this because you are grounding yourself through the breaker box and if there is a problem with the breaker or box then you could get shocked!  Even if the breaker looks like it is OK still flip the breaker all the way off and back on again. I have had many customers over the years that say their circuit breaker is ON and OK, but when I drive to their home and reset the breaker the air conditioner starts!  I hate to charge them a service call when all I had to do is reset a breaker!

2. You have reset the breaker and the outdoor unit still does not come on. You turn the thermostat back down so the air conditioner is supposed to be running and you go back outside to the unit. You can hear a little humming sound, sometimes a “Uggg” inside the unit when power is applied. The “Uggg” is probably the compressor trying to start. You might hear the low voltage contactor humming. You pull the disconnect and disconnect the power to your outdoor air conditioning unit. Please make sure your electrical power is off before working on any air conditioning equipment. You take the door or cover off your outdoor unit’s control box and find that the contactor is engaged meaning that the contactor is getting low voltage from the thermostat and low voltage controls. If the contactor is not engaged (contacts not pulled down) then you have a low voltage problem which could be in the thermostat, thermostat wires or your air conditioner’s safety controls. On some air conditions the manufacturer’s install high and low pressure safety switches to protect the unit if the pressures get too high or too low. If your unit is low on refrigerant the low safety switch will not allow the unit to come on. If your unit is real dirty of if the fan motor stops the high pressure switch will stop the unit until it is reset. If your contactor contacts are not engaged then it could be a thermostat or safety control problem. Please make sure that the batteries are good if your thermostat uses batteries. I have seen low batteries cause this problem.

3. The contactors contacts are closed (engaged). Everything is OK with the contactor.  If the contactors contacts are burnt you might need a new contactor. We sell contactors on the following page. Please Click here if you want to see the contactors we sell. Now you take a look at the capacitor/capacitors and find a bad, swollen run capacitor. If you find that your capacitor is swollen then you have found the problem of why your unit will not run! Congratulations!  EPA stopped allowing manufacturers to produce capacitors with cancer causing PCB’s back in the 1990’s.  Since they stopped allowing the use of PCB’s the capacitors now have a shelf life. Many times I see capacitor problems that will not allow the compressor or the fan to come on . Many times you can clearly see that the capacitor is bad because it is swollen or even blown apart with capacitor oil everywhere! Sometimes you will need a special meter to test the microfarad (MFD) or (uf) rating. “MFD” and “uf” mean the same. Some capacitors will have “MFD” on them and some will use “uf”. Most of the time you can tell the capacitor is bad because it is swollen up. Please see the pictures below for the comparison between a good and bad dual run capacitor. Capacitors are called “Dual” because the capacitor helps run both the fan and the compressor. Dual capacitors will have three areas where wires can be hooked up. The terminals are labeled: Fan, C (Com) and Herm.  If you need a new capacitor we sell capacitors on the following page: Please click her to see all the capacitors we sell index page. You will need to know the MFD rating or uf rating and the voltage rating. This should be clearly visible on the label of the capacitor.  If you do not have a capacitor tester you may be able to take the capacitor to a local appliance repair parts store and ask them to test it for you. We sell a capacitor tester on the following page: Please click here to see the Supco MFD10 capacitor tester we sell.  If you do not know what size capacitor you unit uses you can email us with your unit’s model number and we will try to find out which capacitor your unit uses. Our email address is: support@arnoldservice.com We would love to help you out and have your business!

Bad and Good round capacitor. Capacitor on the left is a dual capacitor.
Bad and Good oval capacitor


192 thoughts on “Problem: Air conditioner outdoor unit will not come on. Nothing happens.

  1. Hi Steve AC stopped working Replaced capacitor & contactor. I’m getting a good reading on the fan motor. All reading are good. Fan on ac unit still won’t run. The fan turns on on the inside but not on the out. Help so confused Ian

    1. Hi Ian! If the fan motor is getting 210 to 240 volts to make it run and it is not running then you must need a new fan motor. I am guessing that your contactor contact will close when your thermostat is calling for cooling and you are getting 24 volts to the contactor coil to make it close. If you are not getting 24 volts to the contactor then you could have a thermostat problem, thermostat battery problem, thermostat wire problem (broken wires) or a low or high-pressure safety switch problem. If this is a heat pump unit then you might have a defrost control board problem that is not allowing the fan to come on. Will the compressor come on and the fan does not come on? If the compressor comes on and not the fan then you probably have a bad fan motor. Send me your outdoor unit’s model number if you would like for me to look up the fan motor part number or any other parts.

  2. Not getting any readings on from the leads from the thermostat at the contactor switch, (which should 24v right?), I have 24v power at the thermostat, but I went ahead and replaced it with a new one. Twice now it has run for an hour or so and then shut off and won’t turn back on when the thermostat clicks.

    1. Hi Jesse!
      Yes, you should be getting 24 to 28 volts to the contactor coil when your thermostat is calling for the air conditioner to be on. This could be one of several problems that could include a thermostat problem, thermostat wire problem (possible broken or loose wire), high or low pressure safety switch problem, time delay relay problem (if equipped), low voltage fuse blown problem, if this is a heat pump it could be a defrost control board problem or a low voltage transformer problem. Please make sure that if your thermostat has batteries that the batteries are good. I would suggest that you start testing with a voltmeter between R and C you should have 24 to 28 volts. If not you have a transformer or broken wire problem. With the thermostat calling for cooling you should have 24 to 28 volts between the Y and C terminals to energize the outdoor contactor. If you do not have 24 volts between Y and C then you either have a thermostat problem or a broken thermostat wire problem. We have a post about this problem on the following page: https://arnoldservice.com/problem-my-air-conditioners-contactor-will-not-engage-i-am-not-getting-24-volts-to-the-contactor-to-make-it-engage-what-could-be-the-problem/ You would need to keep checking for 24 volts between the Y and C wires. Where you stop getting the 24 volts is where the problem is located. I hope you can easily find and fix the problem.
      Steve

  3. All of a suddon my AC stopped working and i heard a buzzing from the fan. I changed the capacitor and it started up and worked for about a half house and then the fan stopped again. If i leave the air off for awhile then turn it back on it will start up and work again but only for like 20 mins to a half hour.

    1. Hi Ryan! This sounds like you probably need a new fan motor or the new capacitor that you installed might be weak. I would like to suggest that you turn the power off to your unit and see if the fan motor is hot. If it is hot then make sure the new capacitor that you installed is good and is the right capacitor for your fan motor. The fan motor label should tell the capacitor used for the motor. If the capacitor is good then you will probably need to purchase and install a new motor. Hope you can easily find and fix the problem. Steve

  4. A/C was working fine. Then I turn the temp up on the thermostat and switch it to off. Go outside, pull out the electric connection before rinsing the coils and unit outside with a garden hose. Replace the electric connector outside. Go inside and switch the thermostat back on and lower the temperature. Now it’s hot. Air is blowing inside, however the unit is not coming on outside. This outside unit is just shy of 2 years old and so I imagine it’s something I did? I’ve done this twice before with no problems. Am I missing something?

    1. Hi AJ! I would suggest that you turn the high voltage power off to your unit again. Open up the control panel on your AC and turn your thermostat so it is calling for the cooling to be on. Check to see if the contactor contacts are closed and energized with 24 volts. If the contactor contacts are not engaged then you may have pulled loose one of the low voltage wires or loosened up one of the connections. I would suggest that if you see any wire nut connections that you make sure the wire nuts and all connections are good and tight. . We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day and weekend! Steve

  5. I am having issues with my AC unit. It started not cooling the house, so we thought the freon was low as due to the last few years, we have had to add freon. added freon and it still isn’t working. Checked capacitor, it was bad, replaced it, still not working, replaced the fan motor on the outside, and had to replace the capacitor again because the one we had just put in was bad. We turn the unit on auto on the inside and it comes on, but the outside fan will not turn. It had been turning the wrong way and we fixed that problem, but not it will not turn. If it does, it turns for so long then slows down and quits. Any suggestions on what else to look for or try?

    1. Hi Dene! Sounds like you may either have a bad fan motor or a fan motor that is too small for the fan blade. Sounds like the motor is over heating because it might be too small. This is my guess. I would suggest making sure that the motor that you replaced is the same horsepower, RPM’s and amps as new motor. The motors should match. You should be hearing the compressor running when the fan motor is not running unless the compressor has over-heated and got out on thermal over-load for protection. I would suggest that you feel the compressor to see if it is hot on top if you do not hear the compressor running. It is real hard on the compressor to run without the condenser fan running. Without the fan running the compressor will run for probably 1 to 2 minutes then go off on high head (make a terrible noise) and if left to run going off on high head will eventually go off completely when it over-heats and goes off on thermal over-load. I would suggest getting the fan to run. If you do not have a volt meter I would like to suggest that you get one so you can test to see where the problem is located. We have an air conditioner troubleshooting flow chart that I hope will help you determine where the problem is: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

      1. Just wondering, does the new fan motor have to be exactly like the old one. Same H/P, volts, RPM, AMPS and everything like that? the old one is RPMs – 1100, the new one is RPMs 1075, AMPS for the new one is 1.5, the old one is 1.4. Thank you!

      2. Hi Dene! The motors should be real close to the same specifications. It would be best if the RPM’s and the horsepower are the same. Motors are sized based on the fan size and pitch of the fan blades. If you are having trouble with a newly installed motor, I would suggest that you find the FLA (Full load Amps) or RLA (Running Load Amps) of the motor. If your new motor is 1.5 amps then the motor should not draw over 1.5 amps or it will over-heat and go off on thermal over load. About the only way to test the amps is with an amprobe meter where you can place the jaws of the meter around one of the wires of the motor while it is running and see on the meter how many amps the motor is using. A good example of an Amprobe meter is on the following page where one is sold on Amazon: https://www.amazon.com/dp/B00OYFGJU2?tag=amz-mkt-chr-us-20&ascsubtag=1ba00-01000-a0049-win70-other-nomod-us000-pcomp-feature-scomp-wm-5&ref=aa_scomp_aapi1 I hope you can find and fix the problem. Steve

  6. Hi Steve,
    Thank you for all the answers and tips on how to troubleshoot our AC’s really helpful.
    My upstair AC stopped blowing cold air, the outdoor unit (fan and compressor) were both off but I can hear a humming noise. I replaced the capacitor with the same one and the compressor/fan started but not blowing cold air, the pipe coming from the compressor doesn’t feel cold compare to my downstair unit. I called AC company to check my refrigerant and said it’s too low and suggested 2 options 1. charge the Freon (R22) and pay $400 or replace the unit $5000, I decided to just charge the Freon and not it’s cooling, don’t know how long it’s going to last as the Tech said there must be a leak in the system and it’ can be seen.
    Last night my downstair AC thermostat was showing 80 deg. and my set point is 76deg. I checked outside unit and both compressor and fan are off, no humming sound, I reset the breaker next to the compressor but no joy. Is there any other breaker apart from this? Reset button? Any suggestion advice will be appreciated.

    Thanks,
    Alvin

    1. Hi Alvin! Thank you so very much for your kind words. There should be another double-pole breaker 30, 40 or 50 amp inside your home’s breaker box. The breaker or disconnect next to the unit only as you probably know turns the power off to the unit if someone wants to work on the unit. There should be another breaker on your home’s breaker box. I would suggest that you get an insulated screw driver so there is not a chance that you get shocked and push in on the contactor’s contacts to see if your unit will start. If you can not get the contactor to engage without manually pushing the contacts down that you either have a thermostat problem, thermostat wire problem (possible broken or loose wire), high or low pressure safety switch problem, time delay relay problem (if equipped), low voltage fuse blown problem, if this is a heat pump it could be a defrost control board problem or a low voltage transformer problem. Since the indoor air handler works then I would not think you have a transformer problem. With the thermostat calling for cooling you should have 24 to 28 volts between the Y and C terminals to energize the outdoor contactor. If you do not have 24 volts between Y and C then you either have a thermostat problem or a broken thermostat wire problem. You would need to keep checking for 24 volts between the Y and C wires. Where you stop getting the 24 volts is where the problem is located. If your unit does not come on after you manually push in on the contactor then you have a high voltage (210-245 volts) problem which could be in your home’s breaker box or high voltage wiring that goes to your air conditioner unit. If you have anymore questions please let me know. I hope you can easily find and fix the problem. Steve

  7. Hi Steve,
    At a loss for a solution and hoping you could help. Very new unit, less than 2 years old. Compressor won’t start but a “click” is heard. The fan won’t move and compressor doesn’t engage but – we found this out accidentally – banging on the top or putting the electrical door back on will get the fan and condenser moving. Sometimes it takes a few knocks… but then eventually this “jump start” method stopped working. The HVAC repair man came out twice and checked the capacitor but it shows none of the signs of being broken and the unit will start again. He checked for loose wires and even took one wire and retightened it. We got the unit going a 2nd time and did an on and an off retest from the thermostat (using the Nest app). Ran through the night but when the thermostat went off, the next day it wouldn’t start again. The Fonz method works now, but I’m hoping for a more civilized, functioning solution.

    1. Hi Frank! Sorry to hear that you are having trouble with your 2 year old air conditioner. If your air conditioner has any electronic control boards inside then the control board could have a loose connection in one of the components. You might need a new control board or time delay relay if equipped. I think this because you say that you can sometimes bang on the side of the unit and it will start. This is a sure sign that there is a loose connection in the unit. I have had lots of questions about Nest thermostats and have found that some of the systems are requiring a higher VA transformer (over 40 VA) to make the Nest thermostat work correctly. I would suggest that you call Nest and tell them your problem and see what they say. I would suggest that you turn your unit on by turning the thermostat down and check to make sure you are getting a minimum of 24 volts to the contactor coil. If you are not getting at least 24 volts then you might need a higher rated transformer above 40 VA. If you want to test and see if the thermostat is a fault you should be able to turn the 24 volt power source off, take three of the thermostat wires loose from the thermostat and twist the Red (power wire), Green (fan relay wire) and Y (yellow AC contactor wire) together, turn the power back on and your air conditioner should run. If it does not run and you have to hit the side to get it started then the thermostat is not the problem. You might try two or three cycles by separating the 3 wires when you want to turn the unit off and tying them together when you want to start the unit again. If the unit works right after several cycles then I would say that you have a thermostat problem or need a new higher powered transformer. Please let me know when you find the solution to your problem so everyone who reads this will know how to fix the problem. Thanks for asking this question. Steve

      1. Hey Steve
        Thanks for your help. I turned out to be a malfunctioning ignition. We changed that and the capacitor and tightened all screws to the unit. Working well now. Maybe overkill, but glad to have it back on after temps consistently in the high 90s.
        Thanks for your response and help!

      2. Glad to hear that you found the problem and got you air conditioner fixed! Yes! I bet you are glad to have your air conditioner back on after that high 90’s heat! Thanks so very much for your kind words and letting us know how you fixed the problem. Steve

  8. Hi Steve, I have an A/C unit with 2 separate thermostat control 2nd & 3rd floor. I installed a smart thermostat on the 2nd floor last night and before I started I had to turn off A/C breaker outside, but once I installed the unit and turn the breaker back on. Both new unit and 3rd floor thermostat did not power on. I wait about 2 hrs and woke up this morning, still no power. Any idea why or something might cause this? Please advise. Thank you so much!

    1. Hi Thomas! Sorry to hear that you are having trouble with the thermostat installation. If you did not turn off both the indoor air handler/furnace and just turned off the outdoor unit then you may have shorted out the low voltage system and blown a fuse because the low voltage power source may have still been on. If you have a fuse on your control board I would check and make sure it is in good shape. You should be able to turn the 24 volt power source off, take three of the thermostat wires loose from one of the thermostats and twist the Red (power wire), Green (fan relay wire) and Y (yellow AC contactor wire) together, turn the power back on and your air conditioner should run. If not you might have a blown fuse on the control board or other problem. Also, another thought is that some of the new thermostats require a more powerful transformer (over 40 VA) to make them work. If you have a weak transformer under 40 VA then this could be the problem. I would suggest checking with a meter to make sure you have a minimum of 24 volts AC between the R and C (com) thermostat wires. I hope you can easily find and fix the problem. Steve

  9. Just to pitch in my 2 cents. My HVAC has also failed today, the thermostat is working fine but the outside unit appears dead. I’ve traced the problem to the contactor contacts that were dirty and brazed with electrical arcing. After reconditioning the surfaces with a bit of very fine sandpaper everything is working fine. So watch out for that too – even when the contactor is engaged it may not be making actual contact.

    1. Thanks so very much Pero for taking your time to share this information with others! God bless you and many thanks! Steve

  10. Hi Steve. I have a two year old Hvac that works during the heat of the day but will not come on at night. You can hear the fan outside kick on but not the compressor. I had a technician come out and when they test it everything is fine and it is cooling. Then come nighttime, it shuts off and won’t come back on until about 10 or 11 the next day. They replaced the thermostat (and checked to make sure it wasn’t programmed to cut off), checked the coolant, compressor and checked the capacitor. Have you ever heard of that? I was doing research and read about a float switch? Is that a possibility?

    1. Hi! If you can hear the out door fan come on and the compressor does not run then it has to be a problem with the compressor. The next time this happens turn the power off to your unit and see if the top of the compressor is hot. The compressor might be going off on internal thermal over-load. This is protection for the compressor so that it does not over-heat and burn the windings out. Most of the time safety controls like a float switch on a condensate pump or drain pan, high or low pressure safety switches would cut the whole outdoor unit off and not allow anything to come on outside. If this is a heat pump unit then maybe you have a defrost control board problem, but usually defrost controls board do not have anything to do with cutting the compressor off and on. If the compressor is not running you would need to find out what the problem is with the compressor not starting. Maybe you have a restriction in the refrigeration cycle that causes the compressor to over-heat and stop. I hope you can find an easy and inexpensive solution to your problem. Steve

  11. Hello Steve,

    I read through most posts, and don’t see any similar to my issue.
    BOTH the central furnace fan and compressor kick on when they are supposed to and remain on, consistently. The R-22 unit, lines, blades etc are all clean. The problem is both lines, in & out of the A/C unit are at ambient temperature, and neither cool nor hot. I would think the compressor would not run if the R22 were too low (pressure safety switch), leading me to believe the issue is likely not a leak. I am guessing it could be a clog in the lines (perhaps clogged dryer filter), and therefore the fliud can’t circulate. Will the system still run if the R22 is low? Can I switch-out the dryer-filter myself (seems solder-sweated to the copper pipe) without HVAC equipment? If there is adequate R22, but it is unable to circulate, I would rhink a symptom would be an excessively “hot” compressor.
    Any insight would be greatly appreciated.

    1. Hi Brian! Some units do not high low and high pressure safety switches. The only way to be sure what the problem is would be to connect gauges to your system and see the low and high side pressures. Most of the time when a unit is running and both lines are ambient temperature then this is a sign that either the compressor is not running or the valves are blown on the compressor and it is not doing what a compressor is suppose to do and that is differentiate between the high and low side. Yes, your system could have a blockage and could cause the compressor to over-heat and go off on thermal over-load. Attaching gauges will tell you what the problem is. Most of the time a clogged filter drier is not the problem. I would not recommend a home owner replacing a filter drier because you would need to reclaim the refrigerant with gauges and a reclaiming machine, have brazing tools to braze the new filter drier back in and a vac pump to pump the system down. Most homeowners do not have these tools. I hope you find and easy inexpensive solution. Thanks for asking the question. Steve

  12. Hi Steve,

    My unit comes on and the temp will drop to the set temp. Cold air is coming out of the vents. The outside unit doesnt shut off after reaching the set temp. It will run for hours and the temp will stay the same. If I raise the temp on thermostat it will shut off. The filters have been cleaned. Any suggestions?

    1. Hi Renee! This could be a problem with your thermostat not shutting off when the desired temperature is reached. It could be loose thermostat wire connection that is causing a false reading on your thermostat. I would suggest making sure all thermostat wire connections all the way out to your outdoor unit are good and tight. If it is hot outside it is normal for air conditioners to run lots if sized properly. If your air conditioner is sized correctly and your out door temperature is above the design temperature then the air conditioner should run pretty much all the time except at night when it cools down. Our design temperature here in Louisville, KY is 93 degrees. So when the temperature outside is 93 or above our AC when sized properly should run pretty much all the time to achieve 72 degrees indoor air temperature. You might need to have your outdoor coil and indoor coil cleaned if you have not done this in a while. I hope you can easily find and fix the problem. Steve

  13. Hi Steve, we are having problems with our AC unit outside. I will try my best to explain the issue correctly. The outside unit is not working at all. But it will blow air inside. We had a friend of ours check the unit with multimeters I believe and he said that the breaker must be off because there was no power going to the unit. But when he looked inside, the breaker was in fact on. He tried flipping the breaker on and off. Still nothing. So he tested the breakers with the mulitmeter and said that every breaker was not getting full power except our water heater and that could possible mean a faulty neutral. And lately our water heater has been not heating. And we have had to flip the breaker once a day to make it heat the water again. So I am just wanting to make sure and get a second opinion on what may be wrong exactly. Help please.

    1. Hi Kayla! This sounds like you have an electrical box problem. I would suggest calling an electrician to find out what the problem is. I hope you can get this fixed soon! God bless you and your family. Steve

  14. Hi Steve, just had our compressor replaced a little over a month ago and today the AC unit will not cool the house. Any ideas where to start or what to check? Thanks for the help.

    1. Hi Ross! Most of the time when a new compressor stops cooling that soon it is caused by a leak and the refrigerant running low, thus letting the compressor over-heat and go off on thermal over-load. I would suggest turning the power off and see if the compressor is hot on top. Another cause would be the wrong size capacitor was used and the compressor has over-heated or if improper installation techniques like not installing filter driers or not evacuating the system proper can cause a compressor to fail. This could be caused by a loose or burnt wire. I would suggest you turn the power off and inspect all wires to make sure they are tight and not burnt. I would suggest that you or you have someone check the refrigerant charge by attaching gauges to your unit. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you can easily find and fix the problem. Steve

  15. Hi Steve! I have a connector that burned up and needs to be replaced. The service tech cannot come for a couple of days. I shut off the power to the outside unit just in case but obviously the air handler is still working inside but not blowing very cold because of the outside unit is off. Is it okay to let the air handler continue to run inside while I wait for them to come replace the connector? Or should I turn everything off? Or should I turn it off and only run the fan? Thanks in advance!

    1. Hi Tim! I would suggest turning the outdoor unit off by pulling the high voltage disconnect and only running the fan. You could place the fan in the “Fan ON” position on the thermostat. Many people run their fan 24 hours a day for weeks so this should not harm your motor. I am sorry that you can not get your unit fixed any sooner. Hope you can stay cool. Steve

  16. Steve, my wife tried to replace our regular thermostat with a basic programmable thermostat and it didn’t work because we had an “extra wire”. The directions said call an HVAC guy for the installation if you have this “extra wire”. So she decided to hook the old thermostat back up exactly as it was and now the thermostat screen is blank/dead, the vents in the house blow room temperature/warm air and the outside unit does not spin. Could this be a fuse near the unit or a circuit breaker that specifically goes to the outside unit? Thanks!

    Greg and Stefani

    1. Hi Greg! So sorry to hear that your air is not working. Yes this could be a fuse on the control board or the circuit breaker. I would suggest checking to see if you have a fuse on the control board to make sure it is OK and turn the breaker completely back off and back on again. Sometimes breakers look like they are on when they are actually blown. Here is a link to a post we have that I hope will help you out: 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/ I hope the following links will help you find and fix the problem: It could be any one of many problems that could cause one of your air conditioners to not work. If you do not have a volt meter I would like to suggest that you get one so you can test to see where the problem is located. We have an air conditioner troubleshooting flow chart that I hope will help you determine where the problem is: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  17. Hi Steve, Thank you for helping so many folks. My 8 years old rooftop heat pump packed AC stops working totally, nothing on, even the blower fan. I put thermostat to FAN and system to OFF and COOL few times, still nothing on. What do you think, and where do I start? Thanks a lot.

    1. Hi Richard! I would start with checking to see if you are getting high voltage power into your unit by testing with a volt meter. Make sure your breakers are on and you are getting high voltage power 220 to 245 volts. If you are getting high voltage power then I would check for low voltage power between R and C you should have 24 to 28 volts AC. If you aren’t getting the low voltage then you might have a blown low voltage fuse or a bad transformer. We have an air conditioner troubleshooting flow chart that I hope will help you determine where the problem is: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day and can find and fix the problem soon! Steve

  18. Hi Steve,
    I have a Rheem Rapm-024JEZ. Just got a new control board, run capacitor, start relay, and start capacitor all replaced. It was running fine for a few days but now I am getting a flashing c on the led display. That code refers to anti short cycle timer but the problem is that I would be stuck on this code for well over 3 minutes and even the test button would not bypass it. Do you have any idea what the problem could be?

    1. Hi Mr. Chum! I am sorry, but I do not know what the problem could be with your unit. If the short cycle timer is the problem maybe you can by-pass the timer and wire directly to the contactor. Most of the time short cycle timers delay the start of the unit for 2 to 3 minutes if power is removed and engaged again. I would suggest making sure that if your thermostat has batteries, make sure the batteries are good. I am sorry, but I am not familiar with your unit model. After looking at our Rheem parts program this looks like a you have a super high efficiency unit with lots of electronics. All that you can go by to troubleshoot is the flash codes. Sorry that I can not help you out. Steve

  19. Hi Steve – thanks for the great post & info! My outside unit completely stopped today around 6pm after working all day (heat wave!). I followed the video below and assumed I had a capacitor issue as you mentioned but when I took the top off I’d actually had a minor fire inside the unit – the part where the wiring comes into (contractor?) has melted wires and is a real mess. Melted the insulation on the top of the unit lid. Is this an easy fix or indicative of a larger problem?
    Thanks again!
    Dougie.

    1. Hi Dougie! Thanks so much for your kind words! Over-heating of wires usually indicates loose connections. The loose wire connection/connections creates arcing and heat. The wires heat up and things begin to melt and short out. I would suggest repairing the damaged wires and contactor. If the contactor is damaged then you will need a new contactor. We sell contactors on the following page: https://arnoldservice.com/product-category/air-conditioner-parts/ac-contactors-heat-pump-contactors/ Then you might need to visit Home Depot or your local hardware store for replacement wires and some solderless connectors. I would suggest that you take part of the burnt wire will you so that you can get a wire size that is close to what you have now. After the repair, hopefully the unit will start up and run fine. If you have any other questions please let me know. I hope you can get your air conditioner fixed soon! Steve

  20. Hi Steve, my outside unit started shutting off and not coming back on unless I reset it. It does this once a day. I reset and it runs all night till it decides to stop the following day. Seems like it didn’t start this until we were having a heat wave. Runs fine at night when its cooler. I’ve replaced thermostat,capacitors,checked contacts and replaced motor. Done everything but check Freon only because I recently had a leak fixed and refilled back in the winter so I assumed it was ok but now I’m wondering. I’ve researched and keep coming up with a pressure switch problem I’m thinking. Any thoughts?

    1. Hi Donnie! I do not know what you are resetting. If you are having to reset the circuit breaker then you probably have a circuit breaker that is going bad. The breaker could be arcing inside and shutting off. I would suggest checking the breaker to see if the outside of the breaker is warm after your unit has run for a while. If the low pressure switch is going off then yes, check your refrigerant charge to make sure it is right. If the high pressure switch is going off the make sure the outdoor unit is clean, unit is charged up correctly (not over-charged) and the fan motor is running up to speed. Might have a fan motor that is going out. I hope you can easily find and fix the problem. Steve

    2. Hello! We suspect our a/c unit stopping cooling because of a dirty filter. It’s bedn in the 70s at night and we shut the furnace off for 8-10 hours and just replaced the filter. We flipped off/on the breaker box switch too. The inside furnace seems to kick on and sounds ok. The outside unit is not. No fan and the compresser sounds like it’s trying to kick on. Is there something specific to the outside unit that may need reset? We have weak cold air coming from the vents. Any harm in letting that run even though the outside unit isn’t functioning ? Happy 4th!

      1. Hi Shelly! I would not recommend allowing the outdoor unit to try and run if the outdoor condenser fan is not running. Is is real hard on the compressor and could damage your compressor over time. I would suggest that you turn off the power to the outdoor unit and inspect the wiring, contactor and capacitor to see if they are in good shape. Many times the capacitor needs replacing and this solves the problem. You might want to try and take the capacitor to a small appliance repair place tomorrow or find a person who has a meter that will test capacitors. If you do not have a volt meter I would like to suggest that you get one so you can test to see where the problem is located. We have an air conditioner troubleshooting flow chart that I hope will help you determine where the problem is: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  21. HELP, I noticed the house getting warm, the outside unit is not working. I can here it click when it tries to engage but will not start. I checked voltage at the Contactor and there is no power. I checked the outside cut off and it is good, I looked inside the Circuit panel and the AC breaker is popped. I tried resetting it and it would not reset. I went out and unplugged the compressor wire harness from the compressor and tried to reset the breaker and it still will not reset. I have the switch in the Attic off I have the outside cut out off and the compressor harness off and the breaker trips to OFF immediately after trying to rest ANY CLUE?

    1. Hi Mr. Hurst! Since you had the compressor unplugged and the breaker is tripping immediately…I would say that you have a short to ground somewhere in your high voltage wiring. This could be inside on your indoor breaker box or in the out door disconnect. You might need to either get an electrician to look at this or if you are comfortable with working on electricity take the breaker box panel off and inspect the wires to see if the short is in the breaker box. This could also be a short in your seal tite that houses the wires from the disconnect to the outdoor unit. I hope you can easily find and fix the problem. Steve

  22. Thank you for the great article, and for all the answers to specific problems. My central air unit has been very finicky about turning on. This problem started at the end of last summer. If I turn on the switch for cold air, it doesn’t go on. But then if I play with it for a while, turning it on and off, sometimes walking away and doing it again eventually it will turn on. I was thinking that this might be an issue with the thermostat and that I should have it replaced, but I’ve never had a problem turning on the furnace. DO you think that I could be right about needing a new thermostat, or do you think it might be something else? Thank you!

    1. Hi Linda! Thank you so very much for your kind words! Yes, this sounds like it could be a thermostat problem. I would suggest that you make sure all thermostat wire connections are good and tight. If your thermostat has batteries make sure the batteries are good. The only sure way to tell if it is a thermostat problem would be to test with a volt meter with the thermostat set to call for cooling (AC On). Use a volt meter set to “Volts AC” and test between the Y and C (com) terminals on your furnace’s control board when the AC will not come on. You should get 24 to 28 volts AC between these two wires. If not then you have a thermostat problem or a loose thermostat wire problem. You should also get 24 volts between the G (green) and C (com) terminals on the control board. The G (green) wire makes the fan run. Here is a good post about thermostat wiring that I hope will help: 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/ I hope you can easily find and fix the problem. Steve

  23. My daughter has an Amana outdoor unit. The yellow wire from the thermostat has AC voltage on it, but the contactor does not close (if I close the contactor myself, the compressor runs fine). The yellow alert light is indicating “high line voltage.” The voltage at the service entrance measures 252.5 volts. My theory is the AC line voltage is too high, and the Amana’s circuit board is protecting the compressor by not allowing the contactor to close. is there anything I can do to the circuit board, or must I just complain to the power company? Thanks

    1. Hi Scott! I would suggest that you call your power company and tell them that your AC unit is getting a “high line voltage” fault and the voltage is 252! I have never see voltages over 245. You should be getting 24 volts between Y and C (com) when your thermostat is calling for cooling. If you aren’t then you could have a thermostat problem or a thermostat wire problem. I hope the power company straightens out the problem and you can get AC again. Thanks for asking this question! Steve

      1. Thanks Steve. I do have 24 volts on the yellow wire. The power company came out and measured 249 volts this morning, saying that was within range (and the AC was working at the time). When I asked if it was possible the voltage could rise to 252.5 v in the late afternoon and evening (the period during which the AC stops working… it always starts working again around 10 pm) he said yes. The power company compensates for high demand during the afternoon and evening by “boosting the power.” So now I’m trying to figure out if I can raise the threshold of the high line voltage trip point by a 0.5 volts or so.

      2. Hi Scott! Sorry, I would not know how to go about raising the trip point threshold. If it was me and I was hot I would probably try to find away to wire around it, but when dealing with electronics this could be hard. I would think that the high voltage is not good on electrical parts especially light bulbs. Sorry that I can not give you any advice on how to eliminate this problem. You might consider a voltage regulator, but I know nothing about them. Here is what I found when I googled the topic: https://www.google.com/search?q=home+voltage+regulator&rlz=1C1ASUM_enUS497US497&oq=home+voltage+&aqs=chrome.1.69i57j0l5.9099j0j8&sourceid=chrome&ie=UTF-8 Steve

  24. Hi Steve,

    I have a Trane Air Handler and my problem is that I turn the T Stat down for cooling and I hear the Fan turn on but nothing on the outside turns on, I have replaced the capacitor, contactor, checked all wiring. What could it be?? Thanks

    Ed

    1. Hi Ed! Is the contactor on the outside unit being energized with 24 volts? Are the contacts closed? Are you getting 210 to 245 volts between L1 and L2 and when the contactor is closed (thermostat calling for cooling) you should be getting 210 to 245 volts between T1 and T2. You might have a thermostat problem if the contactor is not closing or you could be low on charge if you have a low pressure switch that is not closed because your unit is low on charge. Please make sure the batteries are good in your thermostat if your thermostat has batteries. I would suggest that you or you have someone check the refrigerant charge by attaching gauges to your unit. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  25. Hello my name is Heather. On my outside unit my fan won’t spin. It hums and if I give it a little push to start it spinning it will continue to spin just fine. But it won’t start spinning on its own. The capacitor looks fine. What could be wrong with it?

    1. Hi Heather! I would suggest that you have the capacitor tested to make sure that the capacitor is not weak. If the capacitor tests in good condition and up to specs then you probably need a new fan motor. I would suggest that you make sure that the motor is getting 210 to 245 volts from the contactor because a weak contactor could cause a motor to not get the proper voltage to run. I hope you can easily find and fix the problem. Steve

    2. Hi steve,
      I was just reading your response to this gentleman since we have the same problem. Our T1 and T2 are 0 volts. The contractor is pulling in. L1 and L2 are 240 V. What wld we check next? Thanks

      1. Hi Ed! If the contactor is getting 240 volts on L1 and L2 and not on T1 and T2 then you either have a bad contactor or the contactor is not energized or closed. You should be getting 24 volts on the contactor coil to make the contactor coil close the contacts and make the circuit between L1 to T1 and L2 to T2. I hope that you can find the problem. We sell contactors on the following page if you need a contactor: https://arnoldservice.com/product-category/air-conditioner-parts/ac-contactors-heat-pump-contactors/ I hope you can easily find and fix the problem. Steve

  26. Does the capacitor have to charge up before the ac unit will run or should it start immediately? Just changed mine and when I press the plunger on the contactor it runs but stops when released.

    1. Hi Helen! The capacitor should work immediately. It sounds like you have a low voltage problem with the contactor not getting 24 volts to energize the contactor coil. You should be getting 24 to 28 volts AC to the contactor coil to make the contactor engage. Since you are able to push the contactor contacts down and the unit works then I would think you either have a contactor coil that is burnt out or the contactor is not getting the 24 volts. If the contactor is not getting 24 volts to the contactor coil then you might have a thermostat problem, thermostat wire problem (loose or broken wire) low voltage transformer problem, blown fuse on control board or in the low voltage circuit, low or high pressure safety switch that is out because your unit might be low on charge (low pressure switch) or the system has a restriction (High pressure switch). A faulty time delay relay can also cause this problem. I hope you can easily find and fix the problem. Steve

  27. We’ve had mice problems in our condenser unit where they have chewed the wires. This Spring I checked it before the A/C season began and repaired two lines of wires. I thought I was good to go and the A/C was working fine until yesterday. There were pops and arcing inside the condenser unit. I shut the A/C unit off and noticed two more wires that had been chewed through that I missed. These wires were inside the condenser unit going to the compressor. Just the wire casing was damaged and I wrapped both with electrical tape. I turned the A/C back on and the fan worked as per the thermostat setting but the compressor would not turn on. Obviously the shorting has damaged something. What could it have damaged and where should I look or check? Great article BTW!

    1. Hi Dave! I hope not, but the shorting out of the wires may have shorted the windings out in the compressor. About the only way to tell if any damage has been done would be to do an ohm test on the compressor. Here is a link to a real good video that describes how to ohm out a compressor so you can see if the compressor has any internal damage: https://youtu.be/chUZEbLT56Q I hope that your compressor is OK and maybe the short shorted on the compressor’s run capacitor. I would suggest making sure the capacitor is in good condition. Hope you can easily and inexpensively fix the problem. Steve

  28. Thank you for the great article. I’ve searched all over and can’t find exactly what my issue is. My breaker doesn’t actually trip. But if I flip the breaker to “Off”, wait about 5 minutes, then turn it back on, the outside unit will run for a while. But then it stops again, but the air handler is still moving air. I always turn the thermostat off and wait until the fan stops before turning the breaker off. I’m somewhat of a novice DIY guy and just want to check the basics first. If you had to guess, what would you check first?

    1. Hi! Thanks so much for your kind words. I would suggest making sure the breaker is not getting warm which would indicate that it is arcing inside and you need a new breaker. Loose wire connections would also cause the breaker to go off. So check all wire connections after turning the power off. If the contactor is not engaged, not getting 24 volts to the contactor coil then you could have a thermostat problem, high or low safety switch problem. Your unit could be low on refrigerant charge, I would suggest that you or you have someone check the refrigerant charge by attaching gauges to your unit. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  29. Hi Steve , I have a outdoor aluminium unit it runs 10-15mins and the compressor stop running I dont know what is problem pls help .

    1. Hi Kenneth! I would suggest that when the unit goes off check to see if the contactor is energized and getting 24 volts to the contactor coil. If not you could have a thermostat problem or a high or low safety control switch problem. If your unit is dirty, if then fan motor is slow or if your unit has a restriction then the high pressure switch could be cutting the unit off to protect the AC unit from harm. You would need to attach gauges to see what the pressures in your system are running. You might have a weak capacitor that is causing your AC unit to stop. I would suggest checking the capacitor to make sure it is good. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  30. Hello,

    We have a unit running two zones and had a HVAC technician come out for a tune up. The unit was running fine prior to his visit. Well he expressed some concerns with the zoning board while he was there and did some jimmying, well, now the AC unit only comes on during certain times of day typically sometime after 8 AM and turns off sometime prior to 6 PM. I don’t know the exact times because I am work but every time they come out and I come home during the day, the unit works perfectly. However, outside these hours no matter what I do I cannot get the compressor or unit to turn on. I’ve had these guys out like 3 times and am convinced they broke something but I cannot figure it out. The thermostat is on hold temperature and as far as I can tell not programmed to run on a schedule. Any thoughts?

    1. Hi JD! I am sorry, but I do not know much about zoning boards, but it sounds like the techs may have messed something up that has affected your thermostat’s program. Sounds like somehow they have interrupted the cooling circuit on the thermostat wires. I am sorry that I can not be there and test to try and figure out what they did to mess up your air conditioning. I would suggest doing some tests when the air conditioner acts up and turns off to see where the Y wire which controls the outdoor unit is being interrupted. Please let me know when you find the answer. Thanks! Steve

  31. I just bought a home and the previous owner told me she had her son mess with the outside unit well I looked at it and it’s gett power to the contacter and capacitor but theirs two yellow wire that are not connected that go to the high pressure sensor will this make the unit not run? If so where would the wires go to

    1. Hi Deshun! If the two yellow wires actually were connected to the high pressure sensor and now they are not connected to anything then yes this could be why the unit is not running. The high pressure sensor is usually a low voltage (24 volt) switch that cuts the 24 volt power off to the contactor so the unit will not run if the pressure gets too high in the air conditioner’s refrigeration system. I would suggest that you look at the wiring diagram that should be attached to the control box of the unit and see where they have the 2 yellow wires going. If they do go to the high pressure switch, and you determine that the pressure switch is bad with an open circuit and the unit is not running then I would suggest that you join the two yellow wires together temporarily to see if the unit comes on with the wires joined together. Most of the time the two wires go into the high pressure switch and if the pressures get too high the switch will open up and prevent damage to your air conditioning unit. I would suggest that you attach gauges to the unit to make sure that the unit’s pressures are correct so you do not harm the unit if the pressures are actually too high. I hope you can easily find and fix the problem. Steve

    2. Thanks for such great article, I had the same issue with my unit. My unit was going down every week and had my AC tech trying to figure it out. I finally changed the batteries on my thermostat and everything worked!

      1. Fantastic! Glad to hear the fresh batteries solved the problem. Thanks so much for your kind words and for posting this! Steve

  32. I have a ducane furnace and ac system the furnace blower is coming on but the condenser is not I change the contactor and capacitor checked all the wiring everything is good. What could be the problem.

    1. Hi James! Sorry to hear that you are having AC problems. Is the contactor’s contacts engaged (pulled down)? If not you have a low voltage problem that could be caused by the thermostat, thermostat wire (loose or broken), low pressure safety switch (unit could be low on refrigerant) time delay relay problem, etc. If the contactor is engaged and nothing is working then you might have a high voltage problem. You should have 210 to 245 volts on L1 and L2 of the contactor and 210 to 245 volts on T1 and T2 of the contactor when the contactor is energized. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  33. Hi Steve,

    My unit will not run at all. I checked the breaker, checked the compressor and it looked fine. I also checked my condensor and all good. Do you have any ideas? There is no sound at all coming from the unit when it is supposed to be on.

    1. Hi John! Sorry to hear that you are having trouble with your air conditioner coming on. I would suggest that you make sure that the contactor coil is energized with the contacts pulled down on the contactor coil If your contactor coil is not energized with 24 volts then you might have a thermostat problem or a transformer problem. You might have a loose wire or a blown fuse on the control board or transformer. I would suggest that you watch the videos on this post page if you have not already. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you can easily find and fix your air conditioner. Steve

  34. I hope you are still replying to comments – this is the best site I have found so far and I’ve been searching for weeks!

    I have a Goodman GSZ130241BC outdoor unit and the fan and compressor are not coming on. There is no hum or any sound.
    The original issue was that the fan was blowing but the unit was putting out intermittent buzzing sounds. It was also not cooling. I did some research and replaced the contactor switch (same issue). I then replaced the capacitor (same issue). I then watched some video and stupidly tried to copy it without knowing fully what I was doing – they took the common black wire from the defrost control board and stuck it on the contactor switch – my fan did the same then the unit buzzed, then the fan shut off along with he fan inside the house. The “cool” light then blinked on the thermostat.
    I feel like I tripped something but am not sure (a) where to start (b) what order to test things.
    I did replace the defrost board and put back in the original capacitor but nothing.

    There is an external electrical panel for the unit, also an internal one, along with eh main circuit breaker box – all breakers are on. I have a decent voltmeter if I knew what to check? Also read there might be a reset button on the outside unit somewhere.

    Any help would be useful!

    1. Hi Nathaniel! You say that the unit is not making any sound at all right now, but was making buzzing sounds and not cooling earlier. I suspect the the earlier buzzing sounds might be a compressor that is locked and trying to start ever so often. If the compressor is locked you might try a compressor hard start booster like we sell on the following page: https://arnoldservice.com/product/supco-spp6-compressor-hard-start-booster-capacitor/ If you can not get the compressor unlocked unfortunately you will need a new compressor or a new unit. You say that after connecting the common black wire off the defrost board, the unit buzzed then nothing is happening now. If the black wire was the fan wire that went to the fan motor and you attached it to the wrong side of the contactor then this could have burnt the fan motor up and possibly tripped the circuit breaker. I would make sure that your AC circuit breaker has not blown. Sometimes circuit breakers do not look blown when they actually are blown. You would need to reset the breaker. Then you say that now you have No humming or buzzing. My first question would be. Is the contactor energized with 24 volts? If you are not getting 24 volts to the contactor coil then you have a low voltage problem where it could be a bad low voltage transformer on your air handler or furnace, a blown fuse on the control board or somewhere in the low voltage circuit or a thermostat problem or a loose or broken thermostat wire problem or if your unit is low on refrigerant charge then the low pressure safety switch is not allowing the contactor to close. Defective defrost control boards can also cause this problem. If the contactor is not energized (closed) with 24 volts then you would need to find out why and fix this problem first. If the contactor is energized I would recommend testing the high voltage. You should have 220 to 245 volts coming from your home’s disconnect box on L1 and L2 of the contactor and with the contactor energized you should have 220 to 245 volts on T1 and T2 of the contactor. If not then you probably have a bad contactor or you have a blown circuit breaker or loose high voltage wire. I would suggest making sure the fan and compressor are wired correctly according to the unit’s wiring diagram and the label on the side of the fan motor. Sorry for all your trouble. I hope the following troubleshooting links will help you out: https://arnoldservice.com/troubleshooting/ Let me know if you have any more questions. I hope you can easily find and fix the problem. Steve

  35. Hi Steve.
    We recently began running the air conditioning in our house and having not thought to explain to my kids to not directly switch the thermostat on and off but to adjust the temperature and let it slowly come on and go off, they have done the bad deed of having air conditioner wars switching it directly on and off several times a day even sometimes and sure enough now the outside unit won’t switch on and the air that comes in to the house is warm. I have been told by a few people (none with an air conditioner repair experience) that my air conditioning unit froze up but I am a little confused if they mean like as in seized or as in it is icy and frozen literally. I have read about air conditioning units literally freezing but don’t see how that would be the case here and didn’t want to do any further damage by trying any of the things suggested to thaw it out like running the fan with the thermostat off . I am trying to fill a handyman void left by my dad’s recent onset of Alzheimers via YouTube learning but am not even really sure what my air conditioner problem even is other than the outside unit no longer coming on which just isn’t quite enough to help get me anywhere. I appreciate any assistance you may be able to offer and thank everyone reading this in advance for their patience to my ignorance.

    1. Hi Crystalynn! I do not know your exact problem? Does your unit have ice on the evaporator (indoor coil) and line set actually frozen up or is the unit not turning on where nothing happens? I hope the following page links will help you out: . We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ I hope you have a great day and can easily find the solution to your problem! Steve

    2. Sounds like you may be having the same problem as me. You could have a bad relay that needs replacing (contactor)…and due to that going bad you may also need to replace the condenser fan motor. Hope that helps point you in the right direction in your troubleshooting.

  36. Hi Steve,

    I have a two zone central AC split system (Rheem) and am having a problem with one of the units after I turned it couple of weeks back. The condenser unit outside will not turn on. I tried some basic things first like changing the batteries on the thermostat and resetting the circuit breaker but that did not work. I ended up calling an HVAC guy and he suspected that the connector was bad. He replaced the connector with one he had in his truck (not sure if it was the exact model) and the unit turned on but started making some loud noises and then shut off after couple of minutes. He confirmed that the connector was receiving power but stated that the power would not stay on. He then removed the connector and manually jumped the wires and the unit started running. The HVAC guy said he would return in the morning and try another connector and replace the thermostat. The next morning, I noticed that the pipes and compressor outside were frozen. I immediately shut down the unit.

    I decided to call another HVAC guy as I felt that the first HVAC guy was not too knowledgeable. The second HVAC guy tested the freon level and said that it was too low and since the the unit uses R22 Freon, it it not worth spending the morning to finding the leak and adding more Freon (approximately $1500-$2000 according to him). He suggested replacing the condenser and air handler completely and quoted $7,500 for the job.

    It appears that I have two issues – first the unit does not turn on and second its low on Freon. Is it possible that both issues are related? I am leaning towards replacing the unit (after I shop around for a better price), since the unit is about 11-12 years old but wanted to see if there was someway to fix the unit and get another couple of years out of it.

    Appreciate you help in advance.

    1. Hi Manny! Sorry to hear you have had a bad experience with HVAC contractors. It sounds like the problem is that your unit is low on refrigerant charge which uses R22 refrigerant and the low pressure safety switch that you probably have on your unit is not allowing the unit to come on because it is low on refrigerant. Most AC units hold 10 to 12 lbs of refrigerant at the most. R22 Refrigerant wholesale is between $600 to $800 for 30lbs. So after fixing the leak in your unit (more than likely you would need a new evaporator coil which is probably leaking) and adding 10 lbs. of R22 at $30.00 a lb. that would be $300 plus the coil which would be probably another $800 to $1000. Plus you have to think about the damage that was done to the compressor with the unit running low on charge. It is real hard on the compressor if the unit runs low on charge. If it is true that your unit is low on charge then I would have to agree with the 2nd service person that you should install a new unit. If you have a leak that could be easily repaired without replacing the evaporator coil then you might consider the fix. R22 is so expensive! I would recommend that you get another company to check out your unit and then give you a quote if they feel the unit is bad and needs replacing. I would check with your friends to see which company they would recommend or check with the Better Business Bureau for HVAC companies that have an A+ rating. I hope that you can get your AC fixed soon. God bless you and your family. Steve

  37. The contactor is not contacting but when you push the contactor manually, it contacts and the compressor and fan starts working. There no voltage to the contactor coil wire which is the white wire. I am also measuring about 124 V on the white wire input side and 124V on the blk/yel wire out put side of the contactor. The thermostat is good. All wires are hook up. Where do I look next? My complain is , you turn the unit on from the thermostat nothing happens, not even a sound.

    1. Hi Mr. Higgins! The contactor coil as you know should only be getting 24 to 28 volts AC from your thermostat and low voltage transformer. I am thinking that you might have a short to ground in the contactor coil or another system component. I would suggest that you remove the low voltage input wires from the contactor coil and see if you are still getting 124 volts. I have never heard of a contactor getting this much voltage. I am just guessing that maybe you have a contactor problem or a furnace control board problem. I do not know where the high voltage is coming from? You should be getting 24 to 28 volts AC between these connections on your furnace control board. Measure with a meter set to “Volts AC” between R and C (com) you should have 24 volts between R and C at all times the furnace power is on. When the system is calling for cooling you should have 24 volts and with the thermostat calling for cooling (AC ON) between G and C (com)-24 volts, between Y and C (com)-24 volts. If you are not getting 24 to 28 volts AC then there is a short somewhere in the wires (could be thermostat, transformer or high voltage wires) or a component like furnace control board or contactor. I am sorry that I can not be much help on this. If anyone else has had this high voltage experience in the low voltage wires then I hope they will comment. Thanks for your question. Steve

      1. Hello Steve, the gentleman’s post above should be read again… he’s saying that he’s got 124v on both sides of the contactor but he has no voltage on the low voltage (24v) terminals on the contractor coil.

        Possibly a float switch interrupter at the evaporator condensate drain line, low pressure switch in the condensing unit, transformer in air handler/furnace.

      2. Yes, thanks for your advice. Steve

  38. Hi Steve,
    First, you are great ; the questions and comments have been very helpful.
    My problem with the central air is the outside unit. Compressor and fan are not operational. With the thermostat engaged (On), I checked the capacitor, it’s good. And 240Vac to the relay. I found 0Vdc on the coil of the relay. I then disconnected the wire nuts from the 24Vdc line (coming from the thermostat)and i have 27vac.
    Is it low gas problem?
    How can i check?

    1. Hi Reza! Thank you so very much for your kind words! If you have a low pressure safety switch on your air conditioner and the refrigerant in your system is low on charge then the switch will not allow the unit to kick on by cutting the voltage off to the contactor. The only way I know to see if you are low on charge would be to install gauges and check the pressures on the low and high side. A faulty delay on make relay or a compressor that is real hot and has tripped the thermal over-load relay might cause the contactor coil to not get voltage. I would suggest that you try to see where the low voltage wires are running and where the 24 volts stops then this is where the problem is. You can temporarily jump (join the two wires together) that go into the pressure switch if you have one to see if you are low on charge. If you have a heat pump sometimes the defrost control boards will go and and not allow the contactor to get the 24 volts needed to engage. I hope you can easily find and fix the problem. Steve

  39. I have a unit older that runs till the line freezes up now u cleaned everyrhing inside and out turned it on went to bed woke up it was still running and starting to freeze condensate pump on furance has a float i hit that float kicked ut on and the ac unit took a break ill check on it again when i return from work tonite.. i think its not kicking off so its just running till that line freezes then it starts to pump warm air in!

    1. Hi Mike! Most of the time when a unit freezes up it is caused by the unit being low on refrigerant charge or an air flow problem like a dirty filter, slow blower motor (make sure capacitor is good on your blower motor) or a dirty evaporator coil. You said that you cleaned everything so you should be good on the unit being clean. Did you clean the underside of the evaporator coil to make sure it is not dirty? I would suggest that you check the refrigerant charge to make sure your unit is charged up properly. Also clean the condensate pump out so it does not stick anymore. I hope you can easily find and fix the problem.
      Steve

  40. Hi Steve, I was hoping you would be able to help me. I tried searching everywhere for people who have a similar problem, but couldn’t find any solutions. The furnace works fine and the blower continues to circulate air throughout the house, but sometime between late night and early morning the outside condenser shuts off. The inside unit continue to work and the condenser will only turn back on after the thermostat, condenser, and furnace is all powered off and reset. After it resets, it turns back on and can keep the house cooled to 68-70°F no problem on a hot day, but once again sometime during the night the condenser turns off again and doesn’t work until everything is reset.

    1. Hi Jason! This could be a hard one to troubleshoot since the problem occurs in the middle of the night. The first thing that I would look at would be the thermostat to make sure that the batteries (if equipped) are good and make sure the thermostat is not programmed to cut the AC off at a set time. The next thing would be to see if the contactor is energized (pulled down) with 24 volts to the contactor coil when the unit stops during the night. If the contactor is not energized then you have a low voltage problem like a thermostat, loose thermostat wire or a high or low pressure safety switch problem. If there is water in the refrigeration lines the water can freeze and create an obstruction in the refrigeration cycle then that could cause high pressure and cause your unit to shut off with the high pressure safety switch. If the contactor is energized (pulled down) then I would suggest that you turn off the power to the unit and see if the fan motor or compressor are hot. If they are hot then you could be low on charge, the fan motor may be stopping on you or you could have a restriction in the refrigeration system. I would suggest that you check your capacitor to make sure it is in good shape because a weak capacitor can cause the fan or compressor to over-heat. I hope you can easily find and fix the problem. Getting up in the middle of the night most certainly will not be easy! God bless you and your family. Steve

  41. Hi Steve,
    First, you have a GREAT site here; the questions and comments have been very helpful.
    My problem with the central air is the outside unit. Compressor and fan are not operational. With the thermostat engaged (On), I checked the capacitor, it’s good. And 240Vac to the relay. I found 0Vdc on the coil of the relay. I then disconnected the wire nuts from the 24Vdc line (coming from the thermostat), and still read 0Vdc. The inside fan circulating the air is operational. Do you think the wiring is bad? Or the thermostat?
    Thanks in advance,
    Rob S

    1. Hi Rob! Sounds like you either have a bad thermostat or a loose or bad thermostat wire. With the thermostat set for cooling and the air conditioner turned down so the thermostat is calling for cooling, you should get 24 to 28 volts between the C (com) and Y (usually yellow wire) on your control board. The Y wire connection provides power to the outdoor unit’s contactor. If you are not getting 24 volts then you probably have a thermostat problem. If your thermostat has batteries make sure they are good. If you are getting 24 volts AC at Y and C then continue to test until you stop getting the 24 volts and this is where your problem is. The green wire (G) controls the fan blower motor in cooling mode or “FAN ON” mode. So you should have 24 volts between the G and C wire when the Air conditioner is running too. I hope you can easily find and fix the problem. Steve

  42. Hi Steve,
    Thanks for the article.

    I have a Carrier AC unit which came with the house I bought. It is fairly new since the house was built in 2014. I tried turning on the AC and noticed the fan does not spin.

    I’ve unplugged the AC, reset the braker for the AC as well and it still does not turn on. I have tried looking for the reset button but can not seem to find it and I’ve also taken off the panel that shows the capacitor as well.

    In the panel there is a black button (which I dont think is the reset button) and when I push it the AC unit turns on and the fan spins….however when I let go of the button the AC unit stops.

    Any idea what could be wrong?

    Thanks.

    Kevin

    1. Hi Kevin! Sorry to hear that you are having AC problems. I really do not know what black button you are referring to other than I am thinking that it might be the button on top of the contactor. If you haven’t already I would suggest that you test the contactor to see if it is getting 24 to 28 volts to the contactor coil. I would suggest that you watch the Youtube video that is located on this post page which shows how to test the contactor. If the contactor is not getting 24 volts to energized the coil then you could have a problem of being low on refrigerant charge (if your unit has a low pressure safety switch) or you could have a thermostat problem, thermostat wire problem (broken on loose wires) battery low on thermostat problem, delay timed relay problem or a low voltage transformer problem. If you want to send me a picture of the button you are talking about then please send the picture to our email address: arnoldservice@gmail.com. I hope you can easily find and fix the problem. Steve

      1. Thanks Steve, I have emailed you the photo.

        Kevin

      2. Sorry, I did not receive your photo. Please try and send it again to our email address. Thanks! Steve

  43. Hi Steve, My Trane A/C unit is about 11 years old. About a month ago, in the middle of the night, the outside unit stopped running but the air handling unit in the ceiling keep moving uncooled air. I turned the unit to the off position. The next day I called a service man. The outside unit came on hours later outside but the air was not cold, just blowing room temperature air. The service man came out that afternoon and added Freon to the unit. It fixed my unit. Last night the same thing happened. The air was moving but the unit was not working. I turned the unit to off at 4:00 am. The next morning I turned the thermostat to on. The outside unit would not come on but the air was blowing on the inside. I took the control cover off (first time for me) to inspect the outside unit. There was no reset ( that is what I was looking for not knowing what to do). I put the cover back on. It was about 10:00 am or 6 hours later. I turned the unit (which was on off) to on. The outside unit came and an now is running. I don’t want to have this problem in the future. What is wrong with my Trane air conditioning unit ??? I am not an A/C person. Thank you for an answer. Kyle

    1. Hi Kyle! I would suggest that if you do not have a volt meter than you invest in a cheap meter from Home Depot or Lowes so you can test to see if the contactor is getting power to the contactor coil or not when the unit goes off. You should have 24 to 28 volts AC to the contactor coil when your thermostat is calling for cooling. If not you have a low voltage problem like a loose wire, a thermostat problem or maybe your thermostat needs batteries if it has batteries. If the contactor is energized with 24 volts and the contacts are closed and the unit is not running then I would think that the compressor and fan are not getting voltage. I would recommend testing the contactor’s L1 and L2 connections. You should be getting 220 to 245 volts there. Please be careful and not to get grounded out when working with high voltage. With the contactor energized you should be getting 220 to 245 volt between T1 and T2 of the contactor. If you are not getting the 220 volts then you have a contactor problem. The compressor could be over heating if you system is low on charge again. You could have a blockage in your system or a bad TXV valve. You would need to attach gauges to see if the refrigeration system is working properly. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ Let me know if you have any specific questions. Steve

  44. Hey Steve I’m hoping you may be able to help me. I have 240 coming into the unit. And I metered 24 v coming in the contactor. It sucks in like it should but the fan still won’t kick over. Ive checked the fuse inside after watching several YouTube videos and it’s fine. I’ve pinned it down to the unit outside but I’m slightly lost after that. I’m a low voltage guy by trade.

    1. Hi Bryce! I would suggest that you test with a volt meter set to “Volts AC”. You should have 225 to 245 volts on L1 and L2 (power going into your contactor from your home’s disconnect) and with the contactor energized, with the thermostat calling for cooling you should have 225 to 245 volts on T1 and T2 (power going through the contactor). If you are getting the 220 volts on T1 and T2 great, if not you probably need a new contactor. If you are getting the 220 volts out of T1 and T2 and the fan is not running then you either have a bad fan motor, loose wire or a bad capacitor. I would suggest testing the capacitor. If you do not have a capacitor tester you might want to take it somewhere to get tested. I hope you can easily find and fix the problem. Steve

      1. Hey Steve!! Thank you so much for your reply with the weekend!!! After further inspection of the contactor I found a dead bug that lodged its self between cycles not allowing a full connection! She’s up and running like a top!

      2. Fantastic glad to hear that you found the problem and got it fixed! Congratulations! Take Care! Steve

  45. Hi there, I got a plm my central A.C. unit stop working making a ummmmmmm noise and the fan isn’t spinning, I took it apart to check the wires to see any loose but can’t find any plm, so i accidentally put the small cover back on and it slip and touch the wire and the fan is working when I don’t have the cover touching it stop and the hummmmm noise still on, I use the cover to touch it sparks and running so house is cool with the cover box touching the wire. I can’t seem to find any problem with grounding any advice? Thanks

    1. Hi Mr. Wimer! This sounds like you have a loose wire where the “small cover that you put back on” is. I would suggest turning off all the high voltage power and throughly check the wires to make sure all wires are tight. The ummmmm noise is probably either the compressor or fan motor trying to start and not getting enough power because of the loose connection. I would suggest checking the contactor for burnt connections and the capacitor to make sure it is in good shape. I hope you can easily find and fix the problem. Steve

  46. Steve,

    I turned our A/C on for the first time this year yesterday but noticed I wasn’t getting cool air from the registers when I came in the house after doing outside work all day. I went out and found that, like a dummy, I had forgotten to remove the cover I put on the unit during the winter. Of course, the fan couldn’t move air. I could hear the hum of what I think is the compressor running but the fan isn’t running. Hoping that the fan motor might have overload protection, I shut off the A/C and let it cool overnight. I re-set the breaker and then turned on the A/C this morning. Unfortunately, the fan still doesn’t run. Any suggestions you may have would be greatly appreciated.

    Tom Johnston

    1. Hi Tom! So sorry to hear that this happened to you! I have had several people tell me they made the same mistake with starting their unit with the cover on. Like many of my mistakes…I bet you and I will never do this again! I hope that this did not damage you unit. Most compressors and fan motors have thermal overloads they protect them from damage. This is why high pressure safety switches are good in preventing damage to a units because a high pressure safety switch will shut the unit off at the contactor so no damage will occur. I would suggest that you do as in the Youtube video that we have on the following page: https://arnoldservice.com/check-air-conditioning-system-not-working/ I would suggest that you test with a meter to see if the fan motor is getting 220 to 245 volts AC. There should be two power wires that go to the fan motor and you should be able to test with a volt meter across these two wires. If you are getting 220 volts to the motor and it is not running then you either have a bad fan motor or your fan motor is still off on thermal over-load and needs more time to cool down. Sometimes it takes over-night for fan motors and compressors to cool. If the fan motor is hot you might want to turn off the power and cool the motor and compressor down with a garden hose. I hope you can easily find and fix the problem. Steve

      1. Steve,
        Wow! Thank you very much for your incredibly fast response. I really appreciate it. After posting my question, I saw that another person had done the same thing. I missed that when I scanned quickly over some of the questions you received.

        I’ll check the things you mentioned and watch the video.

        You are a true gentleman and a scholar!

        Tom

      2. Thanks so much for your kind words Tom! I hope that you can find an inexpensive easy fix!

      3. Steve,

        I hate to bother you again but I think I found the problem – or at least I found one definite problem. I opened the unit and there are two condensers. One is small and it’s definitely blown. The top is severely domed. I’m assuming it’s for the fan but I’m not sure because this is new to me. It’s a GE 97F9899 35uF 440VAC . But I just noticed that it’s also marked 5uf on the same line so it may be a dual capacitor. Anyway, I found capacitors on Amazon with that part number but the Protection number is different as well as a long number at the bottom. My capacitor is marked Protected P969 but the ones I found on Amazon are marked 10,000 AFC Protected and some aren’t marked with protection at all. They are also physically larger than my capacitor but I doubt if that makes a difference and I can fit a larger one in the unit.

        Please advise.

      4. Hi Tom! No bother at all! Yes, if the capacitor is swollen then it is definitely bad. If the capacitor has three terminals marked Herm, Com and Fan then it is a dual capacitor that works both the fan and compressor. If you had a universal motor installed at some point in time they may have installed a separate capacitor for the motor and did not use the “Fan” part of the dual capacitor. So you might need both capacitors. As long as the specs on the capacitor match 35 MFD/uf 440 volts on the new capacitor then it will work fine. The size does not matter other than you might have to adjust the holding strap or make a holding strap out of plumber’s pipe strap. The 10,000 AFC protected ins good. I hope you get the capacitor from Amazon soon. We do sell capacitors: https://arnoldservice.com/product-category/air-conditioner-parts/air-conditioner-capacitors/ but it would be Tuesday before we could ship since it is the Memorial Day weekend. Hope you have a great Holiday weekend! Steve

      5. Steve,

        Once again, I can’t thank you enough. For my nearly 69 years, I’ve done almost all my own work on everything I’ve ever owned but A/C is just one thing I never really learned about. At least I’ll learn a little bit about A/C now.

        My A/C is a Trane – about 10 years old. No work has been done on it except normal maintenance by me every other spring or so. The label on the other (larger) capacitor says it’s a start capacitor. It’s a bit difficult to read the label because of the way it’s turned but I think it’s marked with something like 135mf to 160mf if I’m reading it correctly. I’ll take that out and test it too later today after discharging it, of course. In the small amount of research I’ve done today, I seem to remember reading something about some fan motors needing a dual capacitor for some reason. I wonder if that’s what I have.

        Being new to this, now I’m wondering why I have a dual capacitor and a “single” capacitor. The small one that I know is bad does have three terminals but I can’t see the markings on top until I take it out. The other (larger) capacitor has two terminals with a resistor between them.

      6. Hi Tom! I learn new things about Air Conditioning and life everyday. That is for sure. Most of the time the black start capacitor is good, but it would not hurt to test it anyway. The black start capacitor helps the compressor initially start up for only a second or two. This start capacitor should be connected in line with a little black box relay that allows the capacitor to jump in and out of the circuit when the compressor starts. You might have two capacitors if you ever had a service company out and they either changed the fan motor out or if they did not have the correct capacitor on the truck for both the fan and the motor. They may have added the extra capacitor to make your system work when it initially had a dual capacitor from the very beginning. I hope this makes since. In other words if the service company found that your existing capacitor was bad and they did not have the right size dual capacitor on the truck for both the fan and compressor, then they used two capacitors so they did not have to make and extra trip and to get your AC back up and running. Here is a link to a pretty good Youtube videos where they try to explain the difference between dual and single capacitors: https://www.youtube.com/results?search_query=dual+capacitor+explained I hope this helps you out. Hope that after you replace the one swollen capacitor you will be back up and running. God bless you and your family. Steve

      7. There is a little black box located near the other capacitor. I didn’t look at it closely but it may very well be a relay. The bad relay has the three markings you mentioned for common, the fan, and the compressor and all terminals have wires hooked to them. The other one has wires to it’s two terminals with a resistor wired between those terminals. I’m wondering if my DVM can test it without removing the resistor. Anyway, I’ll get to that.

        The unit is as it came from the factory with no changes. I know that because the company I bought it from installed the wrong unit (a smaller, less efficient, cheaper one) and when I called them to let them know of their mistake (?), they came out and switched it out with the correct one in seemingly a matter of minutes. It came right out of the box and was installed.

        Darn! What a day to go out! Hot! 🙂

      8. Hi Tom! Most of the time the hard start capacitor and relay are not the problem when the compressor will not start. I think you will need a meter that tests capacitors with a “uf” reading capability to test capacitors. The run capacitor most of the time is the problem when a compressor will not start. Here is link to a Youtube video on install a hard start capacitor and relay: https://www.youtube.com/watch?v=Sd1577g0A0I Sorry that you are having trouble on Memorial Day weekend! Hope that replacing the capacitor will fix your problem. Sometimes Home Depot and Lowes sell capacitors. Best of luck!
        Steve

      9. Steve.

        With your help and advice, I’m back in cool air. It’s been miserably hot these last couple days but my system is running fine now. I would have ordered the capacitor from you because it looks like you have the best prices but Amazon was actually able to deliver today (Memorial Day). While waiting, I cleaned the coils and am I glad I did! They were filthy! I usually clean them every other year but I think it’s been three years. The big problem is that my clothes dryer is vented about five feet from the A/C unit and some fine lint does make it through the filter. So during A/C season, I’m only going to run the dryer when the A/C is off – preferably early in the morning when A/C is off anyway – and I’m going to try to rig up something to catch the fine lint that makes it through the dryer’s lint filter.

        Thank you very much! It’s great that there’s people like you so generous with your time and advice to help us out.

      10. Hi Tom! Fantastic! I am glad you fixed your unit by installing a new capacitor! Thanks so very much for your kind words and for letting me know that your problem is solved. God bless you and your family. Steve

  47. Hi Steve,
    I just installed a 24k 2phase Daizuki mini split system in my sun room.
    Runs perfectly for about an hour, then gives me an F1 error message. Interior unit keeps running but exterior unit stops cooling. F1 error is related to exterior temp. sensor. It appears to to installed fine. Thoughts??
    Thanks so much.
    Steve

    1. Hi Steve! I am sorry, but I know very little about mini-split systems. I would suggest that you contact the manufacturer to see what is going on. It sounds like you might have a defective outdoor temp sensor, but I am just guessing. If you can find the sensor and test it to see if it is opening up then this might be the problem. Sorry that I can only guess and can not be any help. I hope you can find an easy solution to your problem. Steve

  48. Hi Steve, hoping you can help this total novice! I have a 1988 Heil central A/C unit which will not power on. It worked perfectly fine last fall, but once I attempted to flip it back on the other week, it wasn’t working. The inside fan works fine, the breakers aren’t tripped and I did reset them multiple times to be sure. When I go out to the unit itself outside, the fan is off and there’s no buzzing, almost like it’s not getting power. I have read things like check the capacitor or drip pan, and been suggested by a friend to check contactor at the unit, but I guess I’m having trouble figuring out a good way to pinpoint the problem. To make things even a bit more difficult, it seems like figuring out the correct panel to remove on the A/C unit itself is a bit of a challenge as it seems less obvious on my unit than the videos I’ve watched. There’s a heat wave coming up here so if there’s any chance I can DYI, I’d love to hear what your thoughts are!

    1. Hi Mark! Thanks so much for asking this question. I would like to suggest that you turn off the power to your unit by pulling the disconnect and find the control panel cover. The cover should be located close to where the high and low voltage wires enter your outdoor unit. Once you get the cover off I would suggest inspecting the wires for tightness and make sure none of the wires are loose or burnt. Turn your AC on from your indoor thermostat and see if you are getting 24 volts to the contactor. coil. If you do not have a volt meter I would suggest that you purchase one because it is a guess as to what the problem is without troubleshooting with a volt meter. Unfortunately we can not see electricity without a meter. Ha! If your contactor is not energized then this would suggest a low voltage problem which could be a thermostat, thermostat wires, contactor or a safety control that is the problem. You would need to test where the low voltage starts and ends. Where the low voltage ends is probably where the problem is. If the contactor is being energized (contacts closed) then I would turn the high voltage back on by reinserting the disconnect and test with your volt meter L1 and L2 on your contactor to make sure you are getting 220 volts from your home’s power source, then with the contactor energized test between T1 and T2 to make sure you are getting 220 volts going through the contactor. If not you probably have a bad contactor. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ I hope you have a great day! Steve

      1. Thanks Steve, I’m doing my best to follow your advice. My A/C panel happens to face the house so it’s a bit tight in there to see. When I opened up the panel, it was full of leafs/fluff which I had to clean out. Once I cleaned it out, I noticed a yellow wire appeared to be burnt apart and therefore disconnected from itself. I stripped the wire a bit and spliced it hoping that would fix the problem. As it turns out, now not only is the a/c unit not kicking on, but the indoor fan no longer turns on either.

        Do you have any thoughts? I could show you pictures if it’d help? I attempted to check for the 24 volts but I’m not sure if my contactor is attached sideways or if it’s just different from the ones I’ve seen, but I wasn’t quite sure where I should be checking for the 24v on it.

        Thank you!

      2. Hi Mark! I would suggest that you watch the following video if you haven’t watched it yet. Here is a link to the video: https://youtu.be/qUlta3q05IQ The AcServicetech channel has about any AC question you can think of with Youtube videos. If you want to send me pictures you can, but send them to my email address so I can open the pictures. Our email address is: arnoldservice@gmail.com I hope you can find and fix the problem. Steve

  49. HI.. Yesterday the outside compressor unit was not coming on and I was not getting cold air. I checked the breakers and noticed that the
    breakers for the compressor were tripped ( we had a lighting storm the day before so that is what I attributed the tripped breaker to) and when I reset it the compressor came on. Today the compressor was not working so I checked the breaker again and it was in the on position. So I turned the breaker off and then back end — and the compressor came on and is producing cold air. Would appreciate your thoughts on what is causing the problem.
    Thanks.

    1. Hi Nick! Any loose high voltage wires or a breaker that is going bad (contacts arcing internally) can cause the breaker to trip. Also short cycling the unit for the thermostat and not giving the unit enough time for the pressures to equalize can blow a breaker. A weak compressor run capacitor can cause a breaker to trip. A compressor that is tight and running over the FLA rating can cause a breaker to blow. I would suggest that you turn off the high voltage power and make sure all wires going into and out of the breaker are tight. Make sure all wires inside your outdoor unit are tight. After your unit has run for at least a half hour feel the outside black plastic part of the breaker. If the breaker feels warm to touch on the outside then you have arcing inside the breaker and you will need to replace the breaker or it will keep on blowing. I would suggest that you turn off the power and test your unit’s run capacitor to make sure it is up the the correct specs. Please let me know if you have more questions. I hope you can easily find and fix the problem. Steve

  50. Hi Steve! Yesterday my wife turned on the A/C for the first time this season. Sadly, she didn’t realize the condenser was still covered from the winter. Now, the condenser won’t come on, just blowing warm air around. Would this be a safety/trip issue, or is something likely damaged?

    1. Hi Gary!
      It would depend on how long it ran with the cover on it. If it ran for over a day then it could have damaged the compressor. Most of the time compressors have thermal over-load switches that will prevent damage. Sometimes it takes over-night for the compressor to cool down and for the thermal over-load to reset. You might want to try and to cool it down by turning off the power to the unit and running a cold hose over the top of the compressor. I hope the thermal over-load resets and the compressor starts running again. Yes, some units have high pressure over-load switches. You should be able to see if your unit has one by studying the wiring diagram. If it does then hopefully you can reset it and be ready to go. Steve

  51. Hi Steve! Loving all your posts! Perhaps I just don’t know enough about these AC units but I am hoping you can help guide me. I live in the PNW and just turned my AC system to cool after our 8 months of winter weather. I noticed the house wasn’t cooling and was able to trace it back to the outside unit not turning on. Checked the breakers and the fuses by the outside unit and all seemed fine. Took off the cover to the unit and found the diagnostic lights simultaneously blinking which indicates normal operation. There is no sound coming from the unit at all. I have been reading that typically there is a humming sound of it it’s the capacitor that needs replacing. Any ideas where I should start now?

    Thanks so much!

    1. Hi Jessica! Sorry to hear you are having problems with your air conditioner. I would suggest that you look and see if the contactor 24 coil is energized (pulled down) or not. You should have 220 volts between L1 and L2 of the contactor and between T1 and T2 of the contactor when the contactor is energized. If the contactor is not getting 24 volts to the coil and not energized then you might have an open high or low temperature switch, a bad defrost control board, a bad contactor, a loose thermostat wire or bad thermostat. We have lots of troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ If your low pressure switch is open then you might be low on refrigerant charge. I hope you can easily find and fix the problem.
      Steve

  52. Hi Steve,

    First of all, thank you for the excellent information on your site. I am trying to diagnose a problem on my six year old Lennox AC unit. The AC unit cools down the house to set temperature. But the AC unit does not start again when the inside temperature rises unless I reset the high pressure safety switch. I replaced the run capacitor recently thinking it is a bad capacitor. But the problem still persists. Is this a contactor issue or something else? Thanks.

    1. Hi! If you have to reset the high pressure switch then problems that could cause this would be a dirty condenser coil, slow condenser fan motor, an over-charge of refrigerant or a blockage in the refrigeration system like a bad TXV valve or a restrictor piston that is clogged up. This could be a bad high pressure switch, but unlikely. I would suggest trying the easiest solution which is clean the condenser coil real well and make sure your motor capacitor is up to specs. I would suggest installing gauges to see what pressures your unit is running. I hope you can easily find and fix the problem. Steve

  53. Hi, my name is mawuli. My air conditioner outdoor unit will not start. If i push the contactor the compressor will start but the fan does not. The in door is working alright though.

    1. Hi! This sounds like you might have a bad fan motor or a bad motor capacitor. I would suggest that you turn off all the power to your outdoor unit and take the capacitor to be tested to make sure it is in good condition. Some small appliance shops will test capacitors free of charge. I would suggest checking all wire connections to make sure they are good and tight. I would suggest testing to see if the motor is getting 220 to 245 volts when the contactor is energized. If the motor is getting the 220 volts and will not run then I would say you need a new motor. If you want me to look up parts then please send me your units make and model number and I will try to look up the parts for you. Our email address is: arnoldservice@gmail.com. The next problem and question that we must ask is, “Why isn’t the contactor closing to start your outdoor unit?” I would suggest that you do some testing with a volt meter to determine why the contactor is not getting 24 volts to energize the contactor coil or if the contactor coil is getting 24 volts then you will need a new contactor. We have many videos, questions and answers on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ I would suggest starting at the furnace control board with the thermostat calling for cooling and test between Y and C. You should be getting 24 volts from the thermostat between Y and C on your control board. If you are not then you either have a bad thermostat or a broken thermostat wire problem. If you are getting 24 volts between Y and C then continue test all the way out to the outdoor unit. Where the 24 volts stop is where the problem is. I hope you can easily find and fix the problem. Steve

  54. hi my name is mike, and my outside condenser is not turning on, the contactor is not pulling in win the system is turned on. i can push the contactor in manually and the fan will start working, but when i let it go, it just stops

    1. I would suggest that you do some testing with a volt meter to determine why the contactor is not getting 24 volts to energize the contactor coil or if the contactor coil is getting 24 volts then you will need a new contactor. We have many videos, questions and answers on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ I would suggest starting at the furnace control board with the thermostat calling for cooling and test between Y and C. You should be getting 24 volts from the thermostat between Y and C on your control board. If you are not then you either have a bad thermostat or a broken thermostat wire problem. If you are getting 24 volts between Y and C then continue test all the way out to the outdoor unit. Where the 24 volts stop is where the problem is. I hope you can easily find and fix the problem. Steve

  55. Hi I’m Vance, I have a trane 1200 model, the condensor fan will not run in heat or cool mode. I replaced the motor and capacitor four months ago because the motor was noisy. I ohmed the motor and get 70, 20, and 90, so I think the motor is okay. I have 120v across the contactor and also on both sides of the capacitor, and the two wires going to the motor also have 120v. I reinstalled the old noisy motor and capacitor, it too will not run. Could it be the defrost board? Thanks

    1. Hi Vance! You should be getting 220 to 245 volts AC between L1 and L2 on the contactor and when the contactor is energized (thermostat calling for heating or cooling) you should be getting 220 to 245 volts between T1 and T2 on the contactor. If not you could have a bad breaker, blown fuse or a broken wire. The fan motor should be getting 220 volts too between two of the power wires. Yes, if the defrost board supplies power to the fan motor, which most of them do then, yes, you could have a defrost control board problem. If you want me to look up parts please send your unit’s model number to our email address: arnoldservice@gmail.com and I will be glad to look up parts for you. I hope you can easily find and fix the problem. Steve

      1. Thanks, after further checking I found the thermostat part# C137767P01 open, when I bypass it the fan will run. Do sell this part?

      2. Great! Glad you found the problem. I am sorry we do not sell that thermostat. Hope you have a great day! Steve

  56. Hi I’m Gary my heat pump will not come on I’ve put new parts on it and it still won’t work. It trips the breaker soon as I turn the breaker on .I on plugged the fan the works .Could it be the compressor?

    1. Hi Gary! More than likely the breaker is being tripped because the compressor is grounding out. Sorry, I would suggest doing an ohm test on the compressor windings. We show how to do this on the following page: https://arnoldservice.com/problem-compressor-will-not-run/ I hope you do not need a new compressor. Steve

  57. I have to reset the high pressure switch on my outside unit to get the fan to work. I have changed the contactor and capacitor. The fan will run for a few minutes and then shut off. When the fan is not working, the interior of my home will not heat properly causing the inside unit to continually run. Any suggestions would be greatly appreciated. Thanks! David

    1. Hi David! More than likely you need a new fan motor. This could also be a defrost control board problem and not a fan motor problem, but you would need to troubleshoot with a volt meter to determine if you need a new motor or a new defrost board. If the defrost board is delivering power to the fan and the fan is not running then you need a new fan motor. If you would like for me to look up parts then please send your model number to arnoldservice@gmail.com Thanks! Steve

  58. I am selling my rental house. No tennant or power to house for past 6 to 7 months. Had power to house reestablished today and tryed out heat pump. Air handler works fine but there was no cool air. I went to outside unit and found that the double pole 30 had tripped. When I reset, it ran 5 or 6 seconds and tripped again. Then I cut the breakers for the air handler, reset breakers for outdoor unit and it stayed on. Problem is, air handler and outside unit trip each other out. Is this maybe a breaker box problem?

    1. Hi Richard! Sorry to hear that you are having trouble getting your heat pump to work. This sounds like either the outdoor unit’s compressor is locked up or the compressor is grounded out. The reason that the outdoor unit’s breaker is staying on when you turn the indoor breakers off is because the low voltage transformer in located inside the air handler. If you turn the power off to the air handler there will not be any low voltage going to the outdoor heat pump unit to energize the contactor and get it started so it does not blow the breaker. We have several troubleshooting posts that I hope will help you out. Here are the links to the posts: https://arnoldservice.com/problem-compressor-will-not-run/, https://arnoldservice.com/problem-i-am-troubleshooting-my-hvac-problem-and-am-wondering-whether-the-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/ and https://arnoldservice.com/problem-i-installed-the-new-capacitor-and-the-boost-cap-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-pow/ We have lots of troubleshooting advice on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ I hope you can find and fix the problem easily. Steve

    2. I have an air conditioner the contacts do not engage and if I push them in they still did not work the outside unit will hum at the Transformer box when the thermostat keeps trying to kick it on thank you in advance for any information that you can provide for me the reason I am writing this as I was reading other comments and read the one about the hurricane and I really appreciated your Christian response and I knew that you are an honest and sincere man

      1. Hi! If your unit will not turn on even if you manually push the contacts in shows that you must have a high voltage problem. You should be getting 210 to 225 volts between L1 and L2 on your contactor. If you are not then you have a blown circuit breaker, blown fuse or a high voltage wire that is loose or broken. Please be careful when working with electricity. The post that we have should tell about everything that I can think of that might be your problem: https://arnoldservice.com/problem-the-air-conditioner-outdoor-unit-will-not-come-on/ I hope you can easily find and fix the problem.
        Steve

  59. I replaced the compressor contacter (Burnt contacts) and thermostat with a programmable one on a Carrier AC/HP Mod #38yxa036 everything seem to be fine. The next day my sister called and said the compressor was not kicking on. I went downstairs removed the cover on the condenser access panel and it immediately kicked on. I let it run a while and put the access cover back on and it immediately shut off again. I left the access panel off for about 18 hrs just so compressor would continue to run & cool house. My sister just called to tell me that she went into basement and could now see that condenser coils are now iced over where I left the panel off last night

    1. Hi Terry! I am a little confused as to where your condensing unit is located. You say that you went down stairs and removed the cover on the condenser access panel and it immediately kicked on. The condensing unit of course should be located outside. The air handler for the condensing unit should of course be located downstairs in the basement. I looked up your model number and our parts program shows that your unit is a split system heat pump. So you should have an outside unit and an indoor air handle. If the air handler in the basement is freezing up then this could be caused by leaving the cover off the indoor air handler unit. If you leave the cover off the air handler it would reduce air flow across the evaporator coil in the air handler and cause air handler coil to freeze up. If the blower motor on your air handler is turning off with the unit outside running then this would cause the indoor coil to freeze up. A low refrigerant charge would cause the indoor coil to freeze up. It sounds like you might need a new blower motor or blower motor capacitor if the air handler is shutting off with the outdoor unit running. I would suggest not running the downstairs air handler with the blower door off if this is what you are doing. I am sorry if I misunderstood what is happening. I hope you can easily find and fix the problem. Steve

  60. I replaced both condensers and contactor. The motor is running but the fan is not. And the ax is blowing hot air. What is the problem here? Notbit is registering 83 degrees?

    1. Hi Edgar! I am sorry, but I have no definite idea what could be wrong. I do not understand what you mean by “replaced condensers”. I am guessing that you mean capacitors? You say “the motor is running, but the fan is not”. Are you saying that the compressor is running and the condensing unit fan is not running? I would suggest troubleshooting with a volt meter and see if your thermostat is sending 24 volts to the heat sequencer causing the problem with the heat coming on and check and see if the thermostat is sending 24 volts to the contactor to energize the contactor. It would be better if you write back through my email address. Please email me at: arnoldservice@gmail.com.

  61. Hello! My outside AC unit was working fine til the backyard flooded from a hurricane. Once the power was restored, it seemed to be working fine for a few hours. As we were fixing fences, I heard what sounded like a neighbor using a hand drill. It would happen for a few seconds then stop then happen for a few seconds again, etc. I realized it was the AC unit. I touched it, and it was extremely hot to the touch, so I turned the indoor thermostat off. Now it won’t come on at all. I cannot afford a new unit, not even an expensive fix. It did not have the usual him when the capacitor would go bad, but a sound on and off that sounded exactly like a hand drill. Just prior to that, it sounded like a lizard got stuck in the fan, and clanked for a few seconds. I looked but didn’t see anything. Then it started the drill noise, no fan moving, and very hot to touch. Ty for any advice!

    1. Hi Ms.Cobb! Sorry to hear that you had to go through that terrible hurricane and now your AC is not working! We have been praying for you all here in Louisville, KY. Our whole church got down on our knees and prayed for you all! I know that God is with you all! From your description it sounds like you have a condenser fan problem and your outdoor condenser fan is not working. When this happens as you described, the outdoor unit heats up and the compressor makes terrible noises because without the fan the system builds up high pressure until the compressor goes off on high head to protect the unit from blowing up. This is very hard on the AC unit and I would suggest not running the AC until the fan is repaired. The motor probably was burnt out from the water getting inside the motor. I would suggest that you or have someone check the voltage going to the motor. If you have 220 to 245 volts going to the motor and the motor is not working then this is for sure a motor problem. Please be very careful when working around electricity with water on the ground. If you would like for me to look up the part number for the fan please send me your unit’s model number and I will try to give you the fan part number. Please send me the model number at our email address: arnoldservice@gmail.com and I will do what I can. God bless you all in Texas and Florida.

  62. i have replaceed the run capacitor and the unit worked for 1.5 monthsd. now the unit has gone out again nothing happening i replaced the capicastor with a chinees equivalent, or is there some other problem

    1. Hi Mr. Webb! There are many things that can cause an outdoor unit to not come on. I would like to suggest that you go through the Air conditioning troubleshooting flow chart that we have on the following page: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf Here is another page where I tell, “What to check if your air conditioning system is not working”. Here is the link: https://arnoldservice.com/check-air-conditioning-system-not-working/ I would check your breaker first to make sure it has not tripped and then check to see if the contactor contacts are pulled down or energized. If the contactor is not energized by the thermostat then you have a low voltage problem like a thermostat, thermostat wire, open safety control like a low pressure switch (maybe low on refrigerant) or a bad contactor. I hope you can easily find and fix the problem. Steve

  63. Hey Steve,
    I am having a bit of trouble with my AC. Have a Honeywell Thermostat. When I turn the switch to auto or on, the fan will run through the furnace but the unit outside will not kick on. I have replaced the Capacitor and connector outside and when I make contact, both the fan and compressor kick on and operate fully and distribute cool air through the house. As soon as contact is released, the unit cuts out.
    How would I go about troubleshooting from here? Could it be a relay in the furnace to the outside unit?
    It is currently 110 outside with no breeze. Please Help! Thanks, Sean

    1. Hi Sean! Sorry to hear that your contactor will not engage when the thermostat is calling for cooling. We have a post about this problem on the following page: https://arnoldservice.com/problem-my-air-conditioners-contactor-will-not-engage-i-am-not-getting-24-volts-to-the-contactor-to-make-it-engage-what-could-be-the-problem/ I hope this post helps you out. You should be getting 24 to 28 volts AC between the Y (yellow) wire and C (common) wire on your furnace’s control board when the thermostat is calling for cooling. If you aren’t then you might have a thermostat problem or a broken thermostat wire. I would suggest tracing the 24 volt wires, the two wires that go out to your air conditioning unit. Where you stop getting the 24 volts is where the problem is. This could be in a relay or in a low pressure safety switch. It could be a bad contactor coil if the contactor coil is getting 24 volts and the contactor is not pulled down. Your unit could be low on refrigerant if you have a low pressure safety switch thus not allowing the contactor to get 24 volts to be energized. I hope you can easily find and fix the problem. Steve

  64. Hi Steve,

    I need your help. My central air conditioner outside compressor is turning on with the fan but then shutting off after 2 seconds. I called an HVAC technician and he changed the contactor, compacitor to 440, and added a hard start. The compressor and ac started to work for half a day and now is doing the same thing. The compressor and fan would try to turn on and then turns off. He is now saying that my control panel on my furnace is bad. I am not sure what is wrong with my air conditioner system. The technician is saying that my compressor is fine. He also showed me when he manual push the contactor in that the system it begins to run and the fan turns on as well, but when he let go the compressor shuts off. I have also changed all the filters and also added a new battery to my thermostat. Please let me know your thoughts on this.

    1. Hi Andy! Sorry to hear that you are having trouble with you AC unit staying on. When I was doing service work and found this same problem, most of the time the turning off and on after 2 seconds would be caused by a low pressure switch. If your unit is low on refrigerant charge the low pressure switch cuts the contactor (your whole unit off) to protect your unit from running when the system is low on charge. Did your service tech hook up gauges and look at the pressures when the unit starts for those two seconds? If he hooked up gauges it should tell him if the low pressure switch is the problem. Another problem could be if your refrigeration system is stopped up or has a restriction in it. If the high side has a restriction the compressor will pump the low side down quickly and turn the system off. If your service tech hooked up gauges he would be able to see this. Another problem could be if you have a heat pump unit or if your unit has a defrost control board or a delay timer this could be malfunctioning. Most of the time the furnace control board has nothing to do with the outdoor AC unit running other than if you have a super high tech high efficiency two speed furnace and air conditioner. The two speed high efficiency air conditioners are connected sometime connected to the furnace control board. Most of the time the Y (yellow wire) on your thermostat is connected directly to the contactor on your outdoor unit. The yellow wire might be tied together or connected together with the two wires that go out to your outdoor unit at the furnace control board, but the board only serves as a junction for the two wires and has nothing to do with the operation of the outdoor unit. I would suggest that you pull the high voltage disconnect on your outdoor unit, turn your AC on so the furnace blower and the AC outdoor unit would be running if the high voltage disconnect was plugged in. Check to see if the contactor is engaged. If it isn’t engaged then you have a low voltage problem like a thermostat or thermostat wire problem. If the contactor is engaged (contacts pulled down) then you probably have a low pressure switch or other control that is cutting off the low voltage to the contactor when your outdoor unit is plugged back in at the disconnect. I would suggest tracing the low voltage down with a volt meter. Where you stop getting the 24 volts AC to the contactor then this is where your problem is located. I hope you can easily find and fix the problem. Steve

  65. My air and everything was working yesterday morning and my kids was messing with the temp settings and turned it to heat and when I turned it off I tried cutting the air back on and now the fan or air conditioning or heat won’t cut on. I really don’t know what’s going on.

    1. Good morning Jessica! Since you say that your children were messing with the thermostat…I would suggest that you check the breakers in your electrical box. If the children were turning the thermostat up and down, then this could cause short cycling and then this may have blown the circuit breaker that goes to the air conditioner. The AC circuit breaker should be a double pole 30, 40 or 50 amp breaker. Even if the breaker looks like it is ON I would suggest turning it all the way off and back ON again. Do not touch the sides of the breaker box when resetting the breaker. If the furnace is not coming on either then you might have a blown fuse on the control board or the switch on the side of the furnace might be turned off. I would suggest checking the simple fixes first. This could also be a thermostat problem. I would suggest checking the control board with a volt meter set to “volts AC”. You might need to tape the furnace blower door safety switch closed so you can do some testing. With the thermostat calling for cooling you should get 24 to 28 volts AC between the R and C (com) terminals on the control board. You should also get 24 volts between terminals Y and C (com) and G and C (com). If you are not then you have a thermostat problem or a thermostat wire problem. A thermostat wire might be broken. I hope you can easily find and fix the problem. Steve

      1. I have a similar issue. The other day I installed a new thermostat. The ac worked fine. Then I integrated the humidistat into the new thermostat so we would only have one controller instead of two. The ac was on, then I switched to heat and adjusted the humidity level so we could make sure the humidifier activated and was working as it should. Everything was perfect, so I switched the ac back on. Then I realized the air blowing out of our vents was. Or cold. The outside ac unit (Goodman GSX130361EC) is not on). I don’t hear any noises from the outside ac unit as if it’s dead now. The furnace is functioning, thermostat is set to cool and Fan on auto. Is it possible the unit short cycled? Is there a reset button or should I call a repairman? I completely switched off the breakers and furnace “light switch” for roughly an hour. I turned it back on hoping this would reset something, but to no avail the ac unit outside will not turn on and air blowing through the house is just circulating air.

      2. Hi Matt! Sorry to hear that your AC will not turn on. It sounds like the thermostat is the problem. When you hooked up the humidifier to run off the thermostat is might have messed the thermostat up. I would disconnect the humidifier from running off your thermostat. To make sure it is the thermostat I would suggest that you turn the power off at the furnace. Remove the R (red), G (Green) and Y (yellow) from the thermostat. R is the hot wire, G controls the blower on your furnace and Y controls the contactor on the outdoor unit. Tie these three wires together. Turn the power back on to your furnace. If the AC and furnace blower works then it is a problem with your thermostat. If it does not work then it could be a blown fuse on your control board or maybe another component like the contactor coil might be bad. I hope you can easily find and fix the problem. Steve

  66. A couple months ago I noticed that while blowing air our heat pump system really wasn’t cooling the house. I had resigned to not having ac for the summer and given up. Last week it was hot and I figured I would try resetting the breakers and see if that worked, and it did! But only enough to cool the house a couple degrees and then it stopped cooling again. If I reset the breaker it will cool for a while, then stop. Any thoughts? Getting an HVAC company out is going to be hard with the heat wave we are having, and if it’s something we can fix it’d be great to save the money.

    1. Hi Sarah! It sounds like you might have a bad circuit breaker since you say the AC works for a while and then goes off. I am thinking that the circuit breaker might be arcing inside, getting hot and throwing the breaker. Sometimes breakers look like they are “ON” when they are really tripped (OFF). You might need an electrician to replace your breaker. A loose wire in the breaker box or going to your AC will cause high amps and can cause the breaker to trip off. I hope you can easily find and fix the problem. Steve

  67. Hello. We have 2 units that will do nothing. My husband checked the voltage outside at the ac unit breaker box & there is NO power going to it. One unit was installed just last summer & the other is older. AC was working fine. We left for a couple of hours & noticed it was a little warm inside so we decided to set the thermostat a little lower to cool it off. About an hour later, I noticed that the clock was blinking in the bedroom to indicate we had lost power. Temperatures continued to rise inside & we began to troubleshoot. Nothing worked then we decided to check to see if there was power to the breaker box outside & there is no power. Was wondering if this is an AC problem or electrical? Should we call AC personnel or an electrician? Any help would be great!

    1. Hi! If you have not already, please turn your air conditioner’s breakers completely off and back on again. I have seen many times where the breakers will look like they are ON and they are really OFF, so please try resetting your AC’s breakers. Since you do not have power going to your air conditioning units, I would recommend calling an electrician. Some companies employ both electricians and HVAC techs so you might want to find a company that does both electrical work and HVAC work. I hope you can get this fixed right away. I hate to try and sleep in a hot house! God bless you all. Steve

      1. Thank you for a quick reply! Yes, we did check breakers inside & outside last night. We call AC Tech & they confirmed it was an electrical problem. He stated wiring is aluminum & needed to be repaired/replaced. Going to buy fans & window unit(s). I’m in a small town so I don’t know if I will find any. I have 5 little boys (11, 10, 5, 3 & 2) & cannot be with no cooling of some sorts. I believe he said that one of the circuit breakers broken.?.? I mention that everything was off & yet it sounded like the pilot on the furnace for the heater was trying to come on.?.? He checked it out & it needs to be replaced. Oh by the way, we all ready slept in a hot house (last night), who knows how many more nights!

      2. I am so sorry to hear that your family is trying to make it without AC with all those young children! I hope your AC tech can easily find a replacement breaker and he can get your AC going soon. If you have another double pole breaker available in your box that you do not have to use like a dryer, electric stove you might be able to temporarily connect to that breaker to run the AC until he gets a new breaker. You might consider driving to a nearby town that has a Home Depot or Lowes to pick up a breaker unless you are way far away from other larger towns. Sorry, trying to find out a way to get your air back on. Sorry that I can not help. Steve

  68. Hello can you help I have a goodman outside unit that will not run. I have replaced the capacitor and the contactor and have 240 volts going to my fan and compressor , but unit still not working. have ohmed out fan and continuity on compressor. all check out good. fan volts were within two volts of each other and still not working. Ac was working fine, then one day it stopped. Also tried replacing fan motor with a new one and it would not run.Have tried all I know to do and would like to see if you can help. Thanks

    1. Hi Johnny! It sounds like you are getting 240 volts to compressor and fan motor and nothing is coming on. If this is true then I do not understand why nothing is coming on, unless you have an open winding in the compressor or the fan motor wired up wrong. I think it is time to call a service tech to find out what the problem is. I am sorry that I can not give any advice because from your description the fan motor and compressor should be running. I hope you can find an easy solution to this problem. Steve

  69. I have a Rheem a unit.The outside unit turns on but the fan will not run.The shaft wobbles on the fan motor, do you think this could be a bad motor or capacitor.Thanks

    1. Hi Chris! I would suggest testing the capacitor to make sure it is in good shape. If the shaft has lots of play in it then, yes, you probably need a new motor. The best test would be to test the two wires that go to the motor. See if the motor is getting between 210 to 245 volts AC when the unit is supposed to be running. Please be careful when working with live electricity. If the motor is getting 210 to 245 volts and not working then you will need a new motor. Please send me your units model number if you would like for me to look up the motor part number to our email address: support@arnoldservice.com Thanks! Steve

  70. I replace everything condenser motor capacitor and contactor and still it makes a noise from the comperser .When I have the unit in direct pushing down the button on the contacter the unit comes on but when I go inside and turn on the ac from tstat the condser unit does not come on the breaker swith is on

    1. Hi Juan! Sounds like you are not getting 24 volts to the contactor coil. I would suggest setting the thermostat so it is calling for cooling. Test with a volt meter set to “volts AC” between R and C (com) at the control board. You should have 24 to 28 volts between R and C and also between Y and C at your control board. If you are not getting 24 volts between R and C then you probably have a low voltage transformer problem. Might need a new transformer. If you are getting 24 volts between R and C and not Y and C then you probably have a thermostat problem. If you are getting 24 volts between Y and C then continue to test out by the outdoor unit. The place where you stop getting 24 volts then this is where the problem is. If you have a high pressure or low pressure safety switches on your unit then you might be low on charge and the low pressure switch might be causing the contactor not to be energized because your unit is low on charge. I hope you can easily find and fix the problem. Steve

  71. Hope you can help me out. My outside a/c isn’t cutting on, I checked the compositor and replaced the contactor. Inside unit fan works fine. If I hold the contacts down on the contactor it turns on but shuts off as soon as I release it. Any ideas?

    1. Hi Mr. Ramsey! Sorry to hear that you are having trouble with your air conditioner coming on. It sounds like you wired the new contactor up properly because the unit does come on when you hold the contacts down. This sounds like you are not getting 24 volts to the contactor coil to make it engage, or either the coil is bad on the new contactor. I would suggest that you turn your thermostat down so the air conditioner should be running. Set a volt meter to “Volts AC” and test between the two low voltage wires that go into the contactor coil. You should be getting between 24 to 28 volts AC. If you aren’t then I would suggest that you read the following page where we cover this problem: https://arnoldservice.com/problem-my-air-conditioners-contactor-will-not-engage-i-am-not-getting-24-volts-to-the-contactor-to-make-it-engage-what-could-be-the-problem/ If you have any other questions, please ask. I will be glad to try and help.

  72. I have a Bryant outdoor unit that is not starting. The fan or compressor. Relay is good. Capacitor is good. Low voltage Inc stat and indoor furnace components are good. Indoor fan responds excellent. All power sources are good. Tested compressor and have continuity between common and run and also common and start. Again neither compressor or fan starts.

    Where to look or test next.

    1. Hi Jason! Sorry to hear you are having trouble with your AC not starting. You have a very unusual situation since that you say that you have tested just about everything that I can think off and you say everything is in good shape. I would suggest making sure that you are getting the proper high voltage between L1 and L2 on the contactor. Please be careful not to get grounded out (shocked) when working with live electricity. You should be getting 220 to 245 volts AC between L1 and L2 and when the contacts are closed (AC On at the thermostat) you should be getting 220 to 245 volts AC between T1 and T2 on the contactor. If not you have a high voltage problem and you might have a bad circuit breaker or loose wire. You said you tested continuity between Common and run and common and start, but did not say anything about ohms readings between Run and start. Please make sure you do not have an open circuit inside the compressor. I hope you can easily find and fix the problem. Steve

  73. Ac condenser comes on for a minute then shuts off. R22 Low pressure is good runs at 75 but high stays pinned at 200 while the unit is on or off . Breaker tripped a few times I replaced the breaker but still does it. Could the compresser be going bad drawing more running amps causing this?

    1. I would suggest hooking up gauges to check the high and low pressures with the unit running. Many high efficiency units have a liquid line solenoid valve that cuts the liquid line (high side) refrigerant off when the unit stops. This could be why the pressure is staying at 200 when the unit shuts off. Another problem could be a bad thermostatic expansion valve. If your unit has a thermostatic expansion valve then there has been lots of problems with the TXV valves not functioning properly. Something in the refrigeration oil has been damaging the valves. There has been a recall on many of the thermostatic expansion valves. About the only way to tell how many amps your compressor is drawing would be to use a clamp on Amprobe to measure the RLA (Running Load Amps) while the compressor is running. Hooking up the guages and reading the pressures should tell you what the problem is if it is in the refrigeration system. On the electrical side it could be a weak capacitor, slow fan motor, loose wire connection or a thermostat problem that could be causing the unit to shut off. I hope you can easily find and fix the problem. Steve

  74. Last winter we had electric strom that blew out transformer on my heater but they couldn’t check AC unit now it’s warm tried AC and nothing happening can you help me retired senior name Bill Taylor tks

    1. Hi Mr. Taylor!
      We have several troubleshooting pages that deal with your problem. You will need a volt meter to test various air conditioning parts and components. Here are some of the pages: https://arnoldserv.wpengine.com/check-air-conditioning-system-not-working/ We have an Air conditioning troubleshooting flow chart on the following page: https://arnoldserv.wpengine.com/air-conditioning-heat-pump-troubleshooting-simplified/ another page is: https://arnoldserv.wpengine.com/air-conditioning-heat-pump-troubleshooting-simplified/ and the following page:https://arnoldserv.wpengine.com/problem-my-air-conditioners-contactor-will-not-engage-i-am-not-getting-24-volts-to-the-contactor-to-make-it-engage-what-could-be-the-problem/ If you have any questions please email me anytime: support@arnoldservice.com I hope you easily find and fix the problem. Steve

  75. This is one of our first blog posts. I will be happy to try and answer any questions you have. Thanks so much for your interest and support in our website! Hope you have a blessed day! Steve

    1. My capacitor is reading 30v to the fan motor fan is not coming on an I checked my contact I have 220 an I checked the thermostat help please outside unit not working at all an I racked my breakers

      1. 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 or heat pump is calling for cooling or heating? 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 a capacitor problem. Here is a link to our site if you want to purchase a capacitor: Please click here to see the capacitors we sell: https://arnoldserv.wpengine.com/capacitors-sell-index/ You should have at least three wires going to the condenser fan motor and two of the wires when the contactor is closed should be getting 220 to 245 volts to the fan motor. Most of the time the red and black or the black and yellow wires are the wires that carry the 220 volts to the fan motor. The one brown wire or sometimes two brown wires go to the motor run capacitor. Best of luck in finding where the problem is. Steve

    2. This is Sharon I have a York outside unit it won’t shut off house is cooling but after air get right temp and shuts off outside unit won’t shut off

      1. Hi Sharon! Most of the time if your unit will not shut off the problem is because the contactor contacts are welded together. We have a post that talks about 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/ I hope you can easily find and fix the problem. Steve

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