Posted on

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.

Solution: You probably need a new run capacitor. 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.  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


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

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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.

  26. 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

  27. 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

  28. 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

  29. 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

Leave a Reply

Your email address will not be published. Required fields are marked *