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.

For Quick, Honest and Affordable Service, call

Alexander Heating and Air Conditioning

1-919-886-HVAC (4822)

Raleigh Air Conditioner Repair

Holly Springs Air Conditioner Repair

alexander hvac logo

About these ads

304 thoughts on “Common Air Conditioner Capacitor Failure Symptoms

  1. joel

    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.

    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.

  2. 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

    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

      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.

  3. 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 ?

    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.

      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.

  4. 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.

    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.

  5. 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???

    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.

      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

      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

  6. 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

    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

  7. 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.

    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.

      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.

  8. 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.

    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.

  9. 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?

    1. thehvacguy Post author

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

  10. 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.

    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.

  11. 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?

  12. 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?

    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 blow.that fast?,

      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.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s