Common Air Conditioner Capacitor Failure Symptoms

Capacitor Failure Symptoms are sometime harder to identify without the right tools and expertise. Capacitors can be found in several different sizes and shapes. There may be one or multiple capacitors included in your ac with regards to the design. While the most popular capacitors are the types found on circuit boards, the ones most associated with air conditioning will be the bigger capacitors that assist start and run your motors. There are several motors present in an conditioner and heater systems:

  1. Compressor Motor Run Capacitor: Here is the most popular capacitor that fails. Most of the time these are duel capacitors, which means that there are 2 capacitors built into one. A duel capacitor will have three terminals on the top where a single capacitor will simply have two terminals on top.
  2. Outside Fan Motor Run Capacitor: That is the smaller capacitor found with or part of the Compressor Motor Capacitor. It helps start and run the outside fan that blows air through the outside coils.
  3. Indoor Blower Motor Run Capacitor: Similar to the outdoor fan motor capacitor, it is a small, single (two terminals) capacitor that will help start and run the indoor blower motor.
  4. Start Capacitor: Some models include an auxiliary start capacitor that helps jump start the motors. Most are found on the compressor. These are less common.

Why do capacitors go bad

When capacitors go south, they either go out entirely or they decline in strength. The decline is measured in the “capacitance” units called micro farads. When the capacitors are produced, they are labeled with their specifications capacitance and a range +/- from the design capacitance. This range is the allowable operating range, usually labeled in a percentage range, for the capacitor. If the capacitor starts to fail, the capacitance measured will be outside of the labeled range. Sometimes these are difficult to find any symptoms unless you have the proper tools. Warning, there is a risk of severe shock, so do not try this at home.

Diagnosing a bad capacitor

If a capacitor goes out completely, or is severely out of its operating range, it may prevent the motor affiliated with it from running completely. If the compressor motor is not working, then the air conditioner will not cool. If the outside fan is not working the compressor may cause problems and will short cycle or cease working. If the indoor fan stops, you’ll find that there is no air blowing through the vents.

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356 thoughts on “Common Air Conditioner Capacitor Failure Symptoms

  1. Mike

    Greetings, looks like you have been a ton of help for a ton of people! I had trouble with my blower in the handler not starting. When I inspected the air handler, I noticed it was humming and not moving. With a little push start, the blower kicked in and began to work just fine. I would guess that this means the capacitor is going bad. Is that a good assumption? Thank you for your help.

    Reply
    1. thehvacguy Post author

      that would sound like an accurate diagnostics. However since your blower is failing to start it could mean the start of the blower motor bearings going bad.

      Reply
  2. Mayowa

    My Air conditioner is not working fine. The outdoor and indoor fan will start fine and also compressor start. It gets cooling for a while, maybe after 5 to 10 minutes, compressor shuts down and fan still running and in another 10 to 15 minutes, compressor start again and it gets cooling. what could be the reason for the shut out?

    Reply
    1. thehvacguy Post author

      Actually it sounds more serious. Almost like the compressor is overheating, stopping, cooling off, then restarting. The problem could be either low on freon or bad bearings in the compressor. The latter is usually from lack of maintenance.

      Reply
      1. thehvacguy Post author

        No. However a weak capacitor could have definitely contributed to the compressor bearings going bad.

      2. Mayowa

        I also notice that when it about to shut down, it drag down (reduce the output) the stabilizer voltage and releases it when it shut down?

    2. Bill

      Hi, been poking around on the net and found your site. just bought an older home air handler fan turns on fine but outside unit no fan. so I pushed in the contactor and compressor and fan kicked on. It would not stay on until I taped the contactor spring down. cooled house for 3 hours down to 76 then thought it best to untape the contactor spring. I am not sure what to assume
      thanks for any input
      Bill T

      Reply
      1. thehvacguy Post author

        Good that you didn’t leave it that way. It could be the contactor coil is bad but it could also be a safety switch that is there to protect the compressor when the system is low on freon. Call a qualified service company. Don’t play around with it. You could be doing more damage.

  3. Barbara Bernardini

    My outside unit fan is running, and the inside unit is not bowing any air. I installed a rebated capacitor in 2013. I think is the same problem. Shall I get a brand new capacitor

    Reply
      1. thehvacguy Post author

        Corrected** You can buy it and try it but most of the cost is the labor and you won’t save much.

    1. thehvacguy Post author

      It could be that. That would be the least expensive alternative. And if it isn’t the capacitor, well, you have a new one. They do wear out due to many factors such as time in use, temperature, how long it sat on the shelf.

      Reply
  4. Jr

    I have an electric air handler , when I try to turn the ac or heat nothing comes on . Is it the capacitor or contractor

    Reply
  5. jaguarbaba

    Please, I have an issue with my AC, both the outdoor fan and indoor blower are working but, the condenser is not starting. And I have called different AC technician to take a look at it but they couldn’t see any fault. I have also called an Electrician to check the power supply but, he told me there might be a current leakage in between. But my only surprise is that the same thing happens when I use generator set also. Please, I need your help

    Reply
    1. thehvacguy Post author

      Unfortunately your situation is severe and cannot be diagnose without someone there. If the fan on the outside is working, Ivan only be a capacitor, or the compressor is bad. Everything else would also stop the fan.

      Reply
  6. jaguarbaba

    Please, I have an issue with my AC, both the outdoor fan and indoor blower are working but, the condenser is not starting. And I have called different AC technician to take a look at it but they couldn’t see any fault. I have also called an Electrician to check the power supply but, he told me there might be a current leakage in between. But my only surprise is that the same thing happens when I use generator set also. Please, what could be the problem?

    Reply
  7. Jim

    Breaker trips when heat reaches set temp. Motors run fine but breaker is hot when I check it ..this is the inside unit running on regency heat mode.

    Reply
      1. Jim

        Changed breaker an still having same issue… Breaker was burnt badly…Could it be the heater strip causing the breaker to overheat?

      2. thehvacguy Post author

        It sounds like you need an electrician to justify the size breaker and wires for the heat kit and unit you’re using

  8. kathy

    Hi. i have been hearing a blowing sound coming from my unit inside the house. I opened the panel and felt (coolish air) blowing. The unit is completely off and the fan is on auto. What could be causing this issue and should i be concerned?

    thank you

    Reply
    1. thehvacguy Post author

      Yes something is wrong. Worried? No. But you have something to fix before you have heat again. Is it a heat pump or furnace?

      Reply
  9. Jason

    My blower stopped working. You can free spin the fan without any resistance. I thought it would be the capacitor. I’m living in a rental and my landlord told me to call a service tech. He checked the capacitor and said it was fine. He said it is the bearings in the motor and sometimes they can free pin even when the motor is failing. Is this true?

    Reply
    1. thehvacguy Post author

      he’s partly right. The motor would not likely spin freely if the bearings are bad. But from what he describes it’s probably not the bearings but the electrical windings on the magnets.

      Reply
  10. Mark Husereau

    I have an all electric system. The Bonus room heat gets up to temp and the outside unit turns off fine, however the A/C handler unit in the attic – blower motor continues to run. I set the heat to 68 and the cool to 73. I turned the system to off and the outside unit is now off but the blower from the attic is still running and the room has climbed to 79.

    Reply
    1. thehvacguy Post author

      Several things can be wrong with those symptoms. Short in the wires, bad fan relay, bad circuit board (if you have one), or some other control depending on the system. What is the model number?

      Reply
      1. thehvacguy Post author

        It could be a bad circuit board. find the fan relay on the board, its the largest black “T” shaped box with three wires attached. Check to see if it looks melted in any way. If it is, then the board is fried. If not, then it will take some investigation by someone in person to find the root cause.

      1. thehvacguy Post author

        Actually anywhere. Thermostat wires are not out of the question. Thermostat. Or the unit. I wouldnt be able to rule out any without hands on testimg

  11. Jake

    Hello, Was told that my whole outside unit was bad. Because the air was blowing hot, Well the fan would kick on but not the compressor. I thought it may be a recharge. They told me the unit outside was bad. Now they replaced the unit, charged.. It is still blowing hot through the vents. Could it be that my AC outdoor unit was never bad? They then took that unit out, claiming that it wasnt compatible with my handler, even though it was an American standard.. Same EXACT outdoor unit as before,which worked fine for many years.. He comes back with another unit..Installs that one.. Which would be the second he came with. It works now.

    Reply
    1. thehvacguy Post author

      Here’s the thing about the blower, when the system isn’t heating or cooling the only thing it does is to circulate the air and make the person in the home feel cooler as it slightly speeds evaporation. When no one is home, it serves no purpose. Running the fan all the time only increases energy consumption and reduces the life of the fan motor. Leave it set to Auto.

      Reply
      1. BOOKY

        thanks hvacguy, system is currently heating should I still put it in auto? The reason I ask is capacitor went bad last winter and person who fixed it said to let it run so it doesn’t keep kicking on and off

  12. Justin

    Purchased a home in May and now that winter is here, I am having an issue with our outside unit. It seems that it is kicking on and off more than it should. Periodically, it will kick on, run for 15-20 mins then kick off making a rather loud roaring noise, 10 seconds later it will kick back on and run for another 10 minutes or so. However it does not do this roaring noise all the time, but it seems that the unit kicks on at least 3-4 times every hour. Is this a capacitor issue? I have looked at the unit and it has a fan capacitor as well. Thanks for your insight.

    Reply
    1. thehvacguy Post author

      This sounds like you have a heat pump. The noise you hear is the system going into defrost mode. The roaring noise is either the reversing valve or the compressor. The compressor can make what appears to be a roaring noise and the fan on top will stop running. This is a normal function to prevent the outside unit from icing over. It will do this more frequently as the temperatures drop. The lower the temperature the more often it will do this. This is normal. Watch out for it icing over. That would mean the defrost thermostat outside is not operating as designed. But for now, you are good to go. Have the Freon levels checked in the spring when the temperatures are above 65 degrees. You may be slightly low which also would increase the defrost cycle frequency.

      Reply
  13. Jim Middleton

    When I turn my AC the outside fan kick on, but nothing inside, when I turn on my Heater I hear a buzzing/humming sound outside but nothing comes through the vents inside. It is an Intertherm Nordyne 101304 914577H P3RA-48K SC 10+ 45,500 10 50 amp 86 14, I believe it may be the dual run capacitor Intertherm Nordyne Capacitor 50/7.5 uf 370 volt 621697, but not sure. I am not a HVAC guy I am just researching. I was hoping with your vast wealth of knowledge you may enlighten me. Thank you. Jim

    Reply
    1. thehvacguy Post author

      Could be any number of things. However i dont think it it your dual capacitor. That is not related to the indoor blower not working. I would lean more to a dead blower motor.

      Reply
  14. JAMES WISE

    Hi,

    My problem is that I can switch the control panel to air/on and I can feel that its blowing air throughout the house. But if I set it to auto, lets say 69 deg, sometimes heater will come on when the actual temp drops lower than 69 deg. It works that way sometimes but most of the time, even when the actual temp on the panel says 60, heater would not come on. Same thing happend during summer time.

    Could this be because the capacitor is not holding enough electricity to power the heater?

    Thank you in advance.

    James

    Reply
    1. thehvacguy Post author

      Hi James, no it probably is not a capacitor issue. It is more likely a low voltage control problem. Those problems can be very tricky. There is more information needed to narrow down the possibilities which can cause what you’re finding.

      Reply
      1. JAMES WISE

        Thanks for a quick response.

        Are there any steps I can do to track down the issue or is this something that I have to call an HVAC person for?

      2. thehvacguy Post author

        Unfortunately this may be something you have to call a technician for. These can be time consuming and tricky.

  15. joel

    Question
    Our central unit outside is doing nothing.
    The fan wont turn at all.
    But the air blows semi cold inside the house.
    Any help would be appreciated.

    Reply
    1. thehvacguy Post author

      There are several items to check
      1) Are you getting voltage on the control wire?
      2) Are you getting voltage on the power wires?
      3) Is the contactor pulled in?
      4) Is the freon level low?
      5) Is the capacitor good?

      Call a technician. You’re going to need help with this.

      Reply
  16. Ken

    My HVAC compressor and fan don’t come on, no hum, blower inside keeps running nun stop. The dual run capacitor has rusty connections but is not bulging. I disconnected the capacitor wires and tried to sand the rust, left the unit with the power unplugged and the blower switched to off, next day everything worked fine for couple days, now the same problem is happening again with compressor/fan not coming on and blower continuously running. Would the capacitor be bad or is it an electrical/contact issue? Thanks

    Reply
    1. thehvacguy Post author

      Yes. Probably one of the two. This about all I can say without testing the parts. Get a voltmeter check for resistance on the capacitor. OL means it is dead. Also check the voltage at the load side of the contactor when on. It should have ~240

      Reply
      1. Ken

        Will need to buy a voltmeter for sure , Is it possible for the fan and compressor to stop working at the same time because of a bad run capacitor (would that mean the common is bad) and could that cause a communication problem with the blower to keep it running constant? Thanks

      2. thehvacguy Post author

        A bad capacitor on the outside unit for the compressor and condensing fan motor has no effect whatsoever with the indoor blower. Communication between the outside unit and the inside unit is a wholly different low voltage circuit independent of the capacitors. A capacitor can wear out slowly and lose its capacitance typically is one side or the other so you will have one of the two motors not working. However it can also short out internally which would cause both motors to fail.

      3. Ken

        Well it just started fine again , I left the blower switch off overnight and now the HVAC is working fine. Could a capacitor going bad completely stop both fan and compressor and a day later kick back on?

      4. thehvacguy Post author

        Probably not. But not impossible. A capacitor can act like a kick start that the motor needs sometimes to get started. A weak capacitor can actually put opposing forces on the motor causing it to burn out faster.

      5. Ken

        So after the system ran fine and reached target temperature it stopped as it’s supposed to including blower, however when temperature rose back up, it kicked back on the the blower only. Also what I don’t understand when the compressor/fan don’t start the blower keeps running even if I turn the thermostat off. The only way to turn the blower off is by turning it’s switch off. However when the compressor and fan ran fine the blower would turn off when it’s supposed to.

  17. Leonardo

    Hi, I have a blower running all the time on my a/c I remove the wires from my thermostat but the blower still running also I check the relay that controls the blower an is good . What can be the problem ?

    Reply
    1. thehvacguy Post author

      I have run across this problem many times. Typically the blower replay on the circuit board is stuck in the on position usually due to a short melting the wires or connectors and housing of the relay. Check for burn marks around the relay connectors (The relay is the black ‘T” shaped box on the circuit board with three wires connected to it). Replace the board and change any burned or melted wires.

      Reply
      1. alexander1113

        Trying to help my father ou . He has a Goodman heat pum . 3 years ol . He. Turns on the ac. It works fine for about 10 minutes then the blower begins to shut down slowly. And the system won’t respond for several hours after. But then does the same thin . Any advice?

      2. thehvacguy Post author

        Thanks but this isn’t enough info. The motor could be failing, it could be a pressure issue causing the motor to fail or it could be a control board issue. There may be a few other possibilities but would require hands on to narrow the choices.

  18. Andy

    Question: If the capacitor burned out then do you smell smoke when the AC runs? We smelled the burned yesterday when AC was running, and today the thermostat has no power.

    Reply
    1. thehvacguy Post author

      Not normally you would not smell smoke from the capacitor. More often it is a melted fan switch on the circuit board.

      Reply
  19. carol clarke

    My honeywell 3000 goes blank ,rudd unit will not go on,nothing then restarts again anywhere from 1 hr to 3 hrs ? and then unit goes on again.It has happened twice already/ Its wired direct so no batteries are needed.My ac guy told me to put batteries in it so I did and the thermostat came back on ,still no air. He came over when air was running again could not find anything charged me 79.00 and problem is not solved. Fpl electric was in the area and checked voltage, all good,no breakers went off when this happens.He also took frame off breaker box and checked each breaker. Then again one time only , fan went on, unit started up then air stayed on 1 min and shut off??? sporadic..help

    Reply
    1. thehvacguy Post author

      it sounds like you have a short in the wire somewhere which is why the service technician could not find the problem. That one is a difficult one to resolve but can be found through meticulous checking each individual wire disconnected from its components. This investigation takes a long time.

      Reply
      1. thehvacguy Post author

        it could also be a broken light switch that turns the power on and off to the furnace and the wire is just loose and will connect some times but not at other times

    2. carol clarke

      Thank you for responding.It just happened again now so I called my ac guy and he will come over in a few hours.My concern is I hope it doesn’t go back on again before he gets here and leave me with the problem not solved?
      Thanks carol

      Reply
      1. thehvacguy Post author

        Make sure he checks the condensate pan and the furnace disconnect. Then if those are OK check the thermostat and wires for shorts or proper operation

      2. carol clarke

        I appreciate all of your help.The air just went back on again so I had to call the ac guy to cancel him from coming since he could not find the problem the last time .I”m lost

  20. aaron

    What could be the main cause of both indoor and out door units cuts on and off
    frequently after its powered on for 3mins.please help me

    Reply
    1. thehvacguy Post author

      Not enough info provided to diagnose or even begin to diagnose. Sounds like a circuit board issue either in the furnace control board or the zone control board. But it could also be several other minor issues so someone would have to check it out to see which part is causing the system to shut down.

      Check out our website for more info http://www.alexhvac.com

      Reply
  21. Alex

    Hello, I am having an issue with my carrier heat pump and can greatly use some help. The outdoor unit will not run when the thermostat is set for cool. The indoor unit runs so I went outside to check it out. The outdoor unit was not running at all. I manually pushed in the compressor and the unit turned on. I assumed it had to be the contactor coils. I replaced the contactor and still have the same problem. I took an ohm reading after the fact and discovered that my original contactor was good all along. I am now kind of stuff. My multimeter does not measure capacitance. I ohm meter to it and it went up to 80 ohms. I thought that usually it would spike up real high then bottom out at zero. It has been a while since I have studied HVAC. Now I am not sure what step to go forward with now. The fan relay on my circuit board had a small ohm reading. The fact that the unit turns on when I manually engage the contactor is stumping me right now. Any advice would be greatly appreciated. Thanks.

    Reply
    1. thehvacguy Post author

      The problem could be from many different sources. Hands on is the only way to tell. But here are several causes: 1) Low/no freon (leak) 2) Bad low pressure switch, 3) bad defrost circuit board, 4) Condensate tray float switch, 5) SS2 float switch, 6) bad thermostat, 7) short or loose wire in the thermostat wires. It would take me 3-4 pages to tell you how to check all of these so good luck. I’ll save some of these for separate topics some day.

      Reply
      1. Nicole

        The blower motor and run capacitor have to be replaced on my AC unit. Could preventive maintenance have prevented these parts from going out or is it normal wear of an AC unit?

      2. thehvacguy Post author

        Capacitors should be checked annually. When weak they should be replaced. Weak capacitors shorten the life of the motors. Which is probably why your motor needs replacement now.

  22. David

    HI, I am encountering a recent problem with my air conditioner.
    The air-conditioner works fine in the morning but then in the afternoon I noticed that it was not cooling. I went outside to check the unit and noticed that the fan outside was running, however the compressor was not running. Every minute or so, I would hear the compressor trying to start up but then after one or two seconds it would turn off again. If I turn the unit off for a while and then turn it back on again the compressor works fine. I only encounter the problems in the afternoon when the temperature is very high. What could be causing the compressor to give problems during this time but not at other times during the day or night?
    Initially I thought it might be the start capacitor so I ran a check on the capacitor. The capacitor is a 5/35 microfarads +/ -5% and when I measured it I got 4.9/32.1 so I figured that maybe the capacitor was working well enough. I am now wondering if is the compressor that is going bad and that the symptom arises when it is overworked in the hot afternoon but I’m not sure.
    Thanks so much for your opinion.

    Reply
    1. thehvacguy Post author

      Capacitor needs replacing. However, you could be having symptoms of a compressor bearing going bad. Not checking the capacitor and replacing it sooner could have caused the bearings to wear out before their expected life. This is a typical finding we see when the air conditioner is not maintained every year.

      Reply
  23. Q

    I have a Goodman ac unit. The fan is blowing on top of the unit and a rowing noise will cut on and off. Warm air comes out of the vents. What could that be? Is it a easy fix?

    Reply
    1. thehvacguy Post author

      Sounds like you may have problems with your compressor not running. I would check the amp draw on the compressor.

      Reply
  24. Ted

    I appreciate all the info here but so far have not found my particular issue. Back in March I turned off my heat pump and was using window fans as it was rather nice here for a long time. And I wanted to save some money as well. In June it started to heat up here pretty good and I went to turn on the unit to cool things down. Inside handler fan came on in normal time. Did not think much of it until I noticed no cold air from vents about 20 minutes later. Went out side to check the unit to see if it kicked on. Has had problems in the past with blowing out capacitors. The top fan was running fine and quite like normal but no sound of compressor running. Killed power to the unit and waited a few minutes then turned back on to see if it would kick start. No luck but low hum under fan can be heard like compressor is stuck. Went and bought a window unit for the short term as I could not afford to call out a service. Well I finally got around to getting a replacement capacitor to swap out and to test the unit. After installing same, no compressor. Could it be the relay or would you think that the compressor is just dead? Unit is over 15 years old so I am guessing I will need to belly up and replace the system.

    Reply
    1. thehvacguy Post author

      It sure sounds like your compressor is dead. There are two tests to tell for sure, one is to measure the amp load on start. If it exceeds teh RLA rating on the name plate, you are dealing with a locked rotor and the compressor needs to be replaced. If no amps are measured, then you should check the resistance of the windings. Also check connectivity from each winding to ground. If the resistance on the windings is o or OL, then you have a short or open winding. replace the compressor. If the connectivity to ground is found, replace the compressor.

      Reply
  25. Jacob

    I have an old heat pump and yesterday when i got home from work i noticed the fan had stopped spinning. Now, i am not very knowledgeable about hvac systems, but i did some research and i think it may be a bad capacitor (when i turn on the A/C the fan does not spin but it sounds like everything is running, after about 30-60 seconds it shuts off). But when i opened up the panel i found there was no cable attach for “fan”. Is this common?

    Reply
  26. Danielle

    My central air stopped working. I own a lennox. The fan and the compressor are not running. I can get the fan to start with a push but the compressor does not kick in. Could this be a bad capacitor effecting the compressor and stopping it from starting?

    Reply
    1. gordon williams

      Exact same problem..except when i changed capacitor it worked for roughly 24.hours….then it stopped again.
      This time i cant get the fan to spin and.i still.get the humming sound but no compressor or fan action.
      Inside blower working just.fine on fan and heat. What could be the issue?
      What could cause.capacitor.to blow.that fast?,

      Reply
      1. thehvacguy Post author

        Well it may not be the capacitor now. Running on a bad capacitor can damage the other motors. Check the capacitance. Also check the amp draw on the motors as they start. You could have damaged motors on both the fan and compressor. Prevention is the best cure. An annual maintenance program can help prevent major motor failure.

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