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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254 thoughts on “Common Air Conditioner Capacitor Failure Symptoms

  1. Josh

    Quick question, maybe you can help. My AC unit will come on and then the outside fan will stop running after 1-5 minutes. The outside unit will still hum and buzz like it is getting power and trying to power the motor, but the fan just doesn’t turn. Any ideas off the top of your head? Thanks in advance!

    Reply
    1. thehvacguy Post author

      If the fan can sping freely if pushed, then the capacitor. If the fan feels difficult to spin, then the fan motor is bad.

      Reply
  2. Danielle

    My AC unit was replaced (inside and outdoor unit) 2 yrs ago. Capacitor (unit struck by lightning last year) replaced once. Over the past month, the thermostat will be set at 78 but the temp in the house will read 82. After a few hours in mormalizes then for no reason it will go back up to 81 or 82. This is a daily occurrence. I live in Florida so I know the high temps here can affect the capacitors. The outdoor and indoor units fans are both blowing.

    Reply
    1. thehvacguy Post author

      This is a common complaint with air conditioners. Our dispatch just titles it “Not Cooling” and we go from there. The root cause can be so many reasons that there needs to be more information about what pressures, temperatures, air flow, filter status, electrical readings etc that a simple diagnostics over the phone or web is just not possible. Your best bet is to search for a well recommended service company and see if they can send someone out to take a look. Use various referral services such as Yelp, Google Places, BBB, or friends on Facebook. Good luck!

      Reply
  3. ron

    whats wrong with my air conditioner it has trouble starting up but i end up getting it to run and i just had my dirty evaporator coil cleaned on the unit and the unit is less then 1 1/2 years old

    Reply
    1. thehvacguy Post author

      I would need some more information to help. What is having the trouble? The Indoor Blower? The Outdoor compressor? The outdoor fan?
      Thanks

      Reply
  4. Gabrielle Gause

    My AC went out today. It is only four years old. Nothing was working no fan no air blowing through the vents. When I checked the unit I Looked through the top fanblade I saw some ice up and down the left corner. I guess it was a coil. I poured warm water over it until it defrosted. After that the fan was working again but still no air blowing through the vents. When I turned the fan on the on position it stopped working. What could be wrong with my unit?

    Reply
    1. thehvacguy Post author

      First the indoor coil is frozen and will not allow air to pass. First step is to turn the mode switch on your thermostat to off. Then turn the fan switch to on. If after two hours you still do not feel any air flowing through the vents it is probably the blower fan that is not working. If you do feel air but it is warm you are low in refrigerant and probably have a leak. In both cases you should call your repair company.

      Reply
  5. Zaida

    I have service scheduled to come out Monday but I’m hoping you can help give me an idea of what the problem might be. Symptoms are air coming out of vents, when I turn AC on, cold air comes out, outside fan doesn’t move. Found a “quick start capacitor test” which told me to move fan and if it takes off and starts moving by itself, it’s bad start capacitor. That worked! But when I checked 10 minutes later to make sure fan still moving, it’d stopped again. Did test again but this time fan does NOT keep going by itself. Any ideas? Hoping to get some clues so I know how bad the estimate might be come Monday.

    Reply
    1. thehvacguy Post author

      Sounds like the capacitor to me. If you have been running a long time on a bad capacitor you could also have burned out the fan motor. That is what I warn my customers about when they don’t allow me to change a weak capacitor.

      Reply
  6. Shauna

    My ac unit outside is working fine with no issues, however the inside unit will kick on but towards the end of the cycle it starts to shut off and then comes back on, it does this a couple of time and then finishes its cycle and shuts off. It doesnt do this everytime it cycles but it is doing it intermittantly. It’s not freezing up and the air is cold so not sure what it is?

    Reply
    1. thehvacguy Post author

      I would start to look at either the circuit board or the relay controlling the blower motor. You really need someone there to put gauges on the electrical circuits to give you a more affirmative answer.

      Reply
  7. Bernardo Rangel

    I replaced the run start capacitor and the fan started right up bit the air is still hot, could i have connected it wrong. The wires are two orange and two red, i have an american standard allegince 12.

    Reply
    1. thehvacguy Post author

      Which capacitor? Sounds like the compressor capacitor. The air from the blower or the condenser? Condenser should be hot. Inside blower should be cold. Sounds to me you have other issues if the condenser is working and the blower is working and you still have hot air.

      Reply
  8. Sean

    Hi,
    Central air not working since we bought the house. checked it out today and the caps appeared very old. (house built in 1997) shut off power to unit, removed caps and attempted to discharge them but they had no stored power. Both didn’t produce even a slight spark when I shorted them out. Fan runs normal, compressor does not run at all. Any suggestions? Thanks

    Reply
      1. Sean

        Thanks for the fast reply. I live in Az. and these guys here are jammed up. Told me two weeks before they can fit me in. I’ve been an auto tech for 26 years so thought I’d try and figure it out. Thanks again.

      2. thehvacguy Post author

        Go ahead and replace the caps. That would be the easiest to do without a tech.

      3. thehvacguy Post author

        our welcome and sorry to hear about the delays. Keep trying to reach others. I’m sure there are a few who are not so busy.

  9. martijn

    So, tonight our ac unit started blowing warm air. Unit is about 8 yrs old, live in high heat summers and cold winters area. I don’t think the compressor is coming on, but the fan is running inside and outside. Could be a bad compressor capacitator correct? I will test it in the morning if I can locate it. Where can I get one to replace it?

    Reply
    1. thehvacguy Post author

      eBay. But the problem may not be your capacitor. It can get expensive replacing items until you find the problem. Call a technician and have them positively identify the problem.

      Reply
  10. KC

    Well HVAC guy it looks like I may have corrected my problem and after more review the relay should have been replaced first thing. If your air handler is not coming on or running erratic and you can switch from auto to fan to get it to run, I suggest changing the relay first especially if the unit is 10 years old. This part can be bought for as little as $25.00 retail on Amazon or other retail outlets.
    My condenser fan outside has needed to be replaced about every 8 to 10 years. Wholesale this fan (GE 1/3 HP) motor is $30.00 so argue the price if you can. One of my Goodman units (5 Ton AC/ Heat Pump) is coming up on 25 years old as is the air handler. Thanks , KC

    Reply
    1. thehvacguy Post author

      Sometimes the relay is on the circuit board and the only fix would be replacing the circuit board. It really depends on the year, make and model.

      Reply
  11. KC

    AC blower Goodman 9 years old (R22), AC 2 years (HP) old and a 13 seer. Freezing inside blower not running, seemed like thermostat so I changed, worked for awhile. Cools house and then blower doesn’t start and freezes. Go to heat dry out lines and back to cool everything works for awhile. Fan comes on when you switch from auto to on (this didn’t happen with old thermostat).
    Changed capacitor today and will see if it happens again or this did it. Ordered motor but I think it would not be compatible and no 3 point bracket. As said the unit is miss matched for new Freon but did work for 27 months.

    Reply
    1. KC

      Well the capacitor seemed to fix it but no. The unit did it again and I switched to heat mode and the fan and everything else worked fine. I believe the relay (large 1.4 x 2.4 high w/ 5 wires coming out) for the fan was very hot, fan was cool and spins fine, replace relay?

      Reply
      1. thehvacguy Post author

        When it comes to electrical problems like that it’s best to have a technician will look at it sad that youre not replacing parts that don’t need to be replaced. It best to help someone verify that a specific part is not working otherwise you could be replacing parts for several days and spending extra money not necessary.

      2. KC

        I have lost confidence in most AC companies and the techs, I feel ripped off for having the heat pump / ac installed (410) for 4k when you can order it for $950. They assured me that the old air handler (designed for 22r) is fine and this is not so according to other techs. The parts are cheap compared to someone coming to the house and I plan on learning the Freon installation as I have gauges.

      3. thehvacguy Post author

        You can order it for that much but you are violating federal laws if you try to install it yourself. The additional cost is the labor, tools, extraneous materials, warranty and confidence that it is done professionally and will last the full expected life. There are many other component costs that push tha material costs above 50% total retail costs and still those are wholesale prices for the contractor. There is mark up for transportation, labor, overhead that make up the difference. $4K is a fair price for and average 3T straight a/c and coil replacement of an old R22 system.

  12. Jeff

    I have a bryant air conditioner that’s about 12 years old and the condenser capacitor (it has 3 prongs on it) failed about a month ago. I replaced it and it worked fine until today. What could cause it to keep failing?

    Reply
    1. thehvacguy Post author

      There are several reasons capacitors fail. You need to call a technician to get eyes on the unit to figure out the root cause.

      Reply
    2. thehvacguy Post author

      Capacitors fail for many reasons. Here are just a few; 1) Sat on the self too long before it was sold, 2) High outdoor temperatures, 3) Mounted nest to a significant heat source, 4) Power surge, 5) loose wiring connections, 6) exceeded the number of cycles in its life, 7) wrong capacitor rating for the motor associated with it, 8) damaged while being handled, 9) manufacturing defect.

      As you can see, there is no single reason that can be pointed out. They go bad and that is why they are installed to be serviced frequently.

      Reply
  13. Eddie

    I have an a/c unit on a camper that when started runs fine and starts cooling as it should, but after about 10 mins it like the power is cut in half. the condenser fan slows to a crawl and the compressor starts chugging till it over heats and shuts down. any ideas?

    Reply
    1. thehvacguy Post author

      I have not worked on campers so I am not familiar with the equipment. It sounds like bearing issues but I am just guessing with the level of detail you provided.

      Reply
  14. Ron B.

    Great site! My question is about an older lennox heat pump. Had an hvac man over to check the coolant levels, the fan continually worked. He found a burnt wire off the common on the capacitor. Changed wire. System began to cool house for a day then wire burned out again. I changed wire. No cooling. Changed capacitor. No cooling. Through though all this fan works fine. What should I change next? Thank you for your time.

    Reply
    1. thehvacguy Post author

      Apparently there is a problem in either the contact her or the wiring which is causing too much current to flow through the wire to the common on the capacitor which is burning the wire

      Reply
    2. Ron B.

      So i’ve changed the capacitor, wires, contacts and fan motor. unit turns on, air is semi cool into the house. cool blowing out of unit. fan still turns off after a few minutes and turns back on. still not COLD. when i had the hvac guys on a service call they changed the wire, checked the coolent temp and it blew COLD into the house and warm from the unit. Thoughts? I’m already about $400 into this thing and i have a feeling the hvac guys would rather let me change parts all day long than come over on another service call…..even at $86/ 30min.

      Reply
      1. thehvacguy Post author

        Without putting test instruments on the unit, I cannot offer you any more suggestions. This situation isn’t bringing me any new ideas. Better call a technician because there is no substitute for having eyes and hands on the unit.

  15. Patrickw Perry

    I have a blower issue.
    Just out of the blue yesterday my blower stopped working. Turned everything off waited about 5 minutes then turned it back on and my blower ran for a few minutes then shut off. I looked at my blower board and the LED is blinking. No pattern just blinking. Pulled the blower cover and it was warm not hot but warm. There was so much condensation it was unreal. It was on the i nsolated line coming in from the compressor and forming ice. The condenser box was covered in condensation.I checked the drain it was clear and draining. What do you think this could be?

    Reply
    1. thehvacguy Post author

      Check the amp draw on the blower motor. You should be in the 0.5-1.5 amp range. If higher your fan motor is giving up and causing the ice to form on your coil since it is not blowing enough warm air across the coil to keep it from freezing

      Reply
  16. nate richburg

    The posts on the run capacitor are rusted up. Should I clean them off with sandpaper or something? How do I tighten the connections?

    Reply
    1. thehvacguy Post author

      The staycons can be tightened with pliers before putting them back on the posts. I thought you said you replaced the capacitor. How could the posts be rusted already?

      Reply
      1. nate richburg

        I replaced the start capacitor. THe run capacitor is the one where the posts are rusty and there is arcing on start and shutdown

  17. Joe

    Hi. Our 220V Kenmore (8-10 yrs old?) through-the-wall AC: When I start it for the day, the fan comes on instantly; then after some moments, the compressor tries to start, but fails. It waits a short time and tries again. It will cycle this way 3 or 4 times before the compressor starts running, at which time it runs flawlessly the rest of the day. Is this normal behavior, or do we perhaps have a motor start cap getting tired?

    Thanks :)

    Reply
    1. thehvacguy Post author

      It depends, how many amps is the compressor pulling when it tries to start? It could be a capacitor or it could be the compressor bearings wearing out.

      Reply
  18. Art

    I need help. My indoor blower is not running. I only hear a humming/buzzing noise. I checked the blower motor and if I spin it with my hand and then push the start button it will work. Without hand spinning it, it will just buzz/hum and will get very hot. Any idea? Capacitor? Relay?

    Reply
  19. Lorna

    We have a Trane, 2 stage ac/heater. The air is not as cold as it should be. At times, if we have turned it off, then turn it back on, it cools as it should. But if we run it all day/night, the temperature will actually go up, according to the thermostat thermometer. We have had a tech out, he has no clue what is going on. We just checked the outside unit, the big compressor is running, the small compressor is not. The defrost board shows no power to the small compressor. Yesterday when the tech was her, the large compressor was not running. He jumped it, and it worked for a short time. But shortly after he left, the temperature again started going up. Do you have any suggestions?

    Reply
      1. thehvacguy Post author

        My reply to your last comment should point you in the direction to hire someone to diagnose that issue. The person who came and left without diagnosing the problem is probably not someone you should call again. This takes a highly trained technician for those kind of electrical issues. Find a company and ask for s highly trained and NATE certified technician because the problem will take patience and skill, some of the things the one-guy-in-a-truck will not have.

    1. thehvacguy Post author

      I’m sorry but someone really needs to be on site for this one. It sounds like someone would need to have a multimeter and checking various components and signals. Low/high voltage shorts are some of the most difficult issues to resolve. It takes time and a lot of hands on work to diagnose those problems.

      Reply
  20. Ray

    I have just replaced my capacitor on the outdoor unit. As soon as, I flipped the breaker back on the Fan Motor starts up….The thermostat inside the house is set to Auto and Off. Any ideas about what is happening?

    Reply
  21. Jenn

    Hi I have a question for you. Every now and then our fan on the outside unit stops running (usually on 100+ degree days). What would happen if we were at work all day and this would happen. Would there be any significant harm in the unit if we were not home when this happened?

    Reply
    1. thehvacguy Post author

      The compressor would over heat and cut out due to high temperatures and risk significantly shortening the life of the compressor. I don’t think that the problem with your fan is the temperature although that may make the problem worse. It sounds like it could be the bearings in the fan going bad and the internal overload on the fan motor is stopping the fan. In most of these cases, it is time to change the fan motor.

      Reply
  22. Robert

    Mr HVAC, we have a question. What should the high and low pressures be on a 18 Seer, double compressor, 2 stage heat pump, using R22? The air conditioner is not producing air as cold as it always has. The unit is 10 y/o American Standard.

    Reply
    1. thehvacguy Post author

      There are too many extenuating circumstances that you have not provided to be able to answer that question. There is a chart inside the manual for your system that will provide the answer to your question based on different environmental conditions.

      Reply
  23. tommy

    Hello, I have a ten year old unit that up until three weeks ago worked as advertised. I had a tech come out and check the refrigerant and it is good. Big copper line is cold and the fan is blowing, filter is new, and I just cleaned the unit inside and out? it blows but not really cold. I set the thermostat at 76 and it will not get below 84 degrees. The drain is dripping slowly but not as much as usual. I cleaned it also recently. I am at a loss and do not know what to do. The only thing is that is it is not really warm or hot air coming out of the outside fan?

    Reply
    1. thehvacguy Post author

      Sounds like it is a freon issue despite what the tech is telling you. Sometimes the techs don’t know what they are doing and are just winging it. that may have been the case with the one that came out. If it isn’t the refrigerant, then he should have told you what was the problem. You paid for a diagnostic not a answer to “is my refrigerant level right”. You paid for “why is my air conditioner not cooling”. Get him back out and tell you why it isn’t cooling. Free.

      Reply
  24. Bert Love

    I have a Rheem air handler. Over the past two weeks the blower motor inside comes on for about 30 seconds and stops for 2-3 seconds before starting again. At times, especially after sitting through the day or night not running, it won’t start at all. When this happens if I open the handler and close back up, it usually starts blowing but cycles. I have replaced the capacitor, which seemed to fix the problem for a day then started back. Is it likely the board or motor? I have obtained a board and ordered a blower. Was thinking of putting the new board in but worry that if the motor is bad the board may fry. Your thoughts would be greatly appreciated.

    Bert Love

    Reply
    1. thehvacguy Post author

      Here are my thoughts, if you have a variable speed motor, you probably have a problem with the motor controller and this is an expensive motor to replace. If you have a single or three speed motor (has a capacitor) then it sounds like either bearings, relay or circuit board. Most technicians are trained to identify the root cause for each of these and will not go replacing parts that are not failing. I would gladly call a technician and pay the diagnostic charge to be sure I am replacing the correct part and not guessing at which $300 part might be bad.

      Reply
  25. aaron

    Hello I have a Bryant outside unit in a model home that I purchased about a year ago. We have had the local AC repair out 8x now. This is really frustrating… We keep telling them that yes the thermostat keeps set meaning if its set to 74 it will stay at 74. So when they come out they check everything (they say) then it runs really well for maybe 4 – 6 hours then the humidity in the house rises from 50% to 61% +. This is constant they have checked the Freon multiple times had to replace an A-coil twice now. We know when the compressor turns on and when it doesn’t, the compressor turns on and we can actually hear it outside plus the fan is running too, but when the humidity starts to rise and we check the outside unit again we can’t hear the compressor and we tell the AC repair over and over again this is whats happening and they refuse to believe us..
    I checked the outside lines and we know when its working cause I can see condensation of the non insulated copper pipe and downstairs attached the the furnace I can actually see water flowing to the drain. When its not doing its job this doesn’t happen, but the thermostat still keeps set. Can someone please tell me how I can fix this issue and why the AC guys think we are crazy?

    Reply
    1. thehvacguy Post author

      Sounds like the system is over sized and short cycles thereby not having enough time to remove the humidity. I would check with the builder because they should have a load calculation that can verify the appropriate size unit for the heat load.

      Reply
      1. aaron

        Ok, we have several houses in the area that are similar size so I don’t believe that is the issue. What about “long cycles” instead of short cycles? would this be caused because of a bad capacitor for the compressor? I’m just reaching here and trying to trouble shoot myself because now I am waiting for the repair shop to call back, they told me that they have to get authorization from Bryant to replace the whole unit.

        Thank you in advance

      2. thehvacguy Post author

        I still think that the unit if it is running and keeping the house cool but not removing the moisture were talking about a short cycles situation. that’s the only explanation I can think of if the unit is running fine and keeping the house cool.

      3. James R

        Is it possible that the unit could have a sequencer intalled in such a way as to delay the turn on of the blower fan so that some initial dehumidification occurs durring the cycle ( that is, if the cycle is being shortened by the thermostat’s reaction to the temerature.

      4. thehvacguy Post author

        I would say that the probability of that being the case is very low.

      5. Trish

        Actually turned out the coil needed cleaning. Filthy!!! Somehow the old motor made up for it but was probably why it eventually died out. New motor is adjustable??? Tech said it won’t ‘kill itself” so the coil was cleaned and air flow is fine again. :)

      6. thehvacguy Post author

        That is one of the possibilities. Your coil must have been extremely filthy. Change those filters regularly and stay away from the green mesh ones, they allow just too much debris to come through and clog the coils and damage motors.

  26. Nguyen

    Can I substitute capacitor: 5 uf, 80 uf, 370 VAC, +06 -06% 50/60Hz
    with 5 uf, 55 uf,460 VAC, +06 -06% 50/60Hz
    Thanks

    Reply
  27. Khalil Hammid

    My SoluesAir Split AC unit runs/cools normally for about 30-60 mins and then the indoor unit shuts off. Any ideas why? Thanks in advance.

    Reply
  28. RayInIdaho

    Hi HVAC guy! Both inside and outside fans come on, and there is condensation on the un-insulated freon line right at the furnace (but just a few inches up to a flange, and the line is very cold). I just replaced the capacitor because the high side was bad… but I’m not getting cold air out of the vents still (it’s about the same as a fan would produce), but it is blowing. What do you think?

    Reply
    1. thehvacguy Post author

      It depends on which line you are getting the condensation on. The large one or the small one? If the large one, then condensation is normal and that is why it is insulated. If the small one, then we have a problem and need more information. If the large line freezes then you either have a freon restriction or a leak and are low on freon. It sounds like the compressor is running and the fans are running so I would not even suspect a capacitor issue. Since this probably involves freon, you need a EPA licensed technician to come out and check. Only EPA certified professionals are legally allowed to handle freon.

      Reply
    2. Trish Rocco

      Good morning!! Recently we had our motor and capacitor replaced inside the home. The air is blowing cold however the amount of air coming out of the vents is about 60% less than what used to blow from the vents. So now the unit can only cool the house to about 80 degrees and the units runs all day until evening when the outside temp cools and then the house finally cools down. Not sure what this is. Thank you!!

      Reply
      1. thehvacguy Post author

        It sounds like you’re low on refrigerant. When you are low on refrigerant your coil can freeze over reducing your air flow. Have a technician come out and check your refrigerant levels and see if its low and needs more. If you are low it means you have a leak and probably should do something about the leak. Repairing leaks is not cheap and be expected to pay over a thousand dollars to repair the leak.

  29. Ubaldo Padilla

    My blower motor has stopped working. When set to “auto” it does not turn on at all, and when set to “on” it runs for a couple of minutes and then shuts down only to restart after a few minutes. The blower gets very hot and there is a burning smell in the furnace when this happens. I have already changed the capacitor and the problem persist. I believe the motor is bad, but I first want to understand why it only turns on when set to “on.”

    Reply
    1. thehvacguy Post author

      The hot motor is a sign the bearings are going bad. Changing the motor will correct this.

      However, I think you have two problems going on. The fact that it only starts when set to “on” sounds like it could be a circuit board issue. When cooling or heating the signal to cool or heat triggers an internal signal on the circuit board to turn the fan on. This signal is what I am thinking is missing and why I think the circuit board is having a problem. When the thermostat fan switch is set to “on” another signal goes out the green wire to turn on the fan. This is a separate signal to turn on the fan whenever the heat or cool signal is not sent so that you can circulate the air. This signal appears to be working. So my experience would tell me to check the signal from the circuit board to see if the fan is actually getting voltage when the thermostat is cooling or heating the home. If no signal, then change the board.

      Reply
  30. laney

    I hope I can ask here.
    My blower fan stopped working and when i try to turn it on it makes a humming buzz noise but does not turn on the blower, capacitor? tested it seemed ok but not the fastest jump so i replace it anyway and it works!! later i turn it off to change filter and the original issue returns, humming buzz with no blower on. if i remove the blower and reinstall it works until turned off!?
    any ideas of root cause? dirty motor causing load issues?

    Reply
  31. Channon

    Hello. We recently moved and our air conditioning unit traveled with us. We had it installed, It worked for a day, and then it stopped running so we changed the capacitator on the outside unit and it seemed to solve the problem for a few days. And then it stopped again, and my husband thought it was because he bought a cheap quality capacitator, so we bought a better quality one, which again solved the problem for a few days. Then there was a storm and the electricity went on and off for a second and that stopped it again. Now the capacitator works for maybe half an hour and then stops again for several hours. We can start it again after a few hours and it will work for an hour or so and stop again. We bought a third capacitator, which didn’t work at all. Sometimes we switch between the capacitators that we purchased (as well as the original that came with the machine) and it will work and stop again a bit later. Specifically, the unit outside shudders, stops humming and the indoor part just blows air into the house. The fan outside moves when pushed by a stick. Our capacitator is 35+1.5 and 450 vac if that information helps at all.
    We are wondering if it is an electrical issue because obviously changing the capacitator isn’t solving the problem.
    Thanks for your time!

    Reply
    1. thehvacguy Post author

      Sounds like the fan relay is going bad or possibly shorting out. That is an easy replacement. The capacitor shoul be rated per the fan motor and not the wiring diagram. If the motor calls for one capacitance, use that capacitance as it is a function of the motor and the motor could have been replaced with a universal motor or a different motor than the one on the wiring diagram.

      Reply
  32. James R

    I’ve been working one an older coleman suncutter model hvac unit for a mobile home and have been having poor luck with the blower. It seems it will occasionally cut on and blow for a random amount of time, cold or hot depending on the setting. But the blower fan will kust stop and it usually can be turned back on without waiting for a little while. Capacitance reading on the blower motor capacitor was half of what the wiring diagram recommends so I’ve ordered new capacitors for it as well as the compressor and condense fan since they looked like they were in terrible shape. What else could be causing this issue?

    Reply
    1. James R

      Replaced the capacitors and tidied up the wiring. I’m thinking the fan relay is bad. Bypassing the relay to the correct side of the fuzes, I got the blower to turn on when the breaker is turned on. Compressor and external fan are working well on the new dual run cap. Everything checks out except the blower relay.

      Reply
    2. James R

      I thought I would summarize my experience a little better since it was mostly the post commentary that helped me solve the problems.

      The initial symptoms where that only heat would work, and that the cooling was intermittent. Upon inspecting I found that blower capacitor was only holding half it’s rating. The fan spun freely but wasn’t getting any power. I couldn’t activate the heat because it was 90 or so outside and 95 inside and the thermostat knew better. So I noted this and checked the rest of the unit. I found that the other capacitors to the compressor and condenser fan were at rating, but one was badly deteriorated and sitting in a damp area. The wiring was done on these in such a way that figuring out where the condenser fan was getting it’s power from was difficult.

      I replaced that two capacitors with a dual run capacitor and the one on the blower motor. This solved the wiring nightmare and got the capacitors for the condenser fan and the compressor out of the bottom of the unit where rainwater or condensate was forming. I still couldn’t get the blower motor to come on via the thermostat so I bypassed the blower relay and hooked it up directly to the fuze panel ( component side ) to see if the blower even functioned at all. And it did. So I left it like that and instructed the homeowner on how to turn the fan off if need be and got their house cool until I could get a blower relay ( it was a Saturday evening ).

      So it turns out that the blower relay was bad ( 5 terminal ). By having a normally connected pin powereing the fan when the heating strips are turned on, this was bypassing the blower fan relay function and turning the blower on ( for safety reasons ).

      Replacing the 5 terminal blower fan with a like-rated and same styled relay has everything working properly now. This was a pro bono/absque/ut enim job, so replacing a couple of old capacitors wasn’t a billing baloon and the wiring wasn’t done well for the blower fan in the old configuration.

      Thanks again!

      Reply
  33. Gary Yung

    Hello, my central air unit isn’t turning on. I replaced the fuses and turned on the thermostat, then I heard a loud humming sound coming from the outdoor unit. I went to check and the fan wasn’t turning on even if I nudged it. Also, there was “steam/condensation” coming from the bottom of it for a minute or so. Could it be a bad capacitor? I hooked it up to my multimeter on Ohms setting and got nothing but I do get a reading when I set it to read Voltage. The capacitor has no signs of bulging. What could be the problem(s)? Thanks!

    Reply
    1. thehvacguy Post author

      You have a locked fan motor. Replace the fan motor and get a new capacitor. Good luck!

      Reply
      1. Gary Yung

        I just got my capacitor tested and it’s good. Turns out my multimeter doesn’t measure Farads! Anyways, could a bad fan motor cause the fuses to blow? Also, is the condensation issue normal? Thank you for the quick response!

      2. Gary Yung

        When you say “locked fan motor” do you mean that the blades won’t spin even when nudged? The fan blades spin freely when I push it.

      3. thehvacguy Post author

        I thought you said it didnt turn freely. Then the motor is shorted out but it is the motor that is tripping the fuse. Check the amp draw when you start it and you should see it spike on start up. It shouldn’t be more than 1-1.5 amps

  34. Jimmy

    Hey there Hvac guy……I have an Amana AC unit outside and I have “push spin” the fan and the motor works fine. I realize this more than likely the capacitor. Problem is kind sir I have 2 separate cylindrical capacitors one black with 2 connections and one grey with multiple connections…Black is 145-174 MFD Grey is 35/5 MFD………..Can you tell me which is which? Thanks in advance Amana model # RCB30B2A…………

    Reply
    1. thehvacguy Post author

      The 35/5 with multiple wires. Careful that little puppy can hold a charge even with the power off. The black one is a start capacitor with an inline resistor that takes it out of circuit once the compressor is running.

      Reply
  35. Marcus Tan

    My Panasonic CS-C12GKH indoor unit fan blower does not run according to the designated speed. If I set it to High fan speed, somehow it doesn’t respond accordingly & maintain at the lower fan speed.
    But at times the fan blower will suddenly run at high fan speed which it supposed to have been running when set earlier on.
    What is the cause to such fan speed behavior?

    Reply
    1. thehvacguy Post author

      The fan is a variable speed fan that adjusts the speed based on internal friction rates in the duct system. It adjusts itself with an internal amp sensor on the fan

      Reply
      1. Sway

        My home ac will run fine for about 30 minutes or so and then it will stop blowing air out of vent but outside fan and unit is still on. I can set the fan on the tstat from auto to on and it will turn back on but it is not cold. I would have to turn off cool for a few minutes then turn it back on for it to work. Could it be a bad capacitor??

      2. thehvacguy Post author

        An intermittent problem like that does tend to be a capacitor issue, but it could be a loose wire, or a problem circuit board in the air handler.

      3. Sway

        My home ac will run fine for about 30 minutes or so and then it will stop blowing air out of vent but outside fan and unit is still on. I can set the fan on the tstat from auto to on and it will turn back on but it is not cold. I would have to turn off cool for a few minutes then turn it back on for it to work. Could it be a bad capacitor??

        I checked the wiring and nothing seems loose. Do you suggest replacing the circuit board before a capacitor even tho fan does turn right on if I turn off cool and turn it back on after a few minutes.

      4. thehvacguy Post author

        I personally would not start guessing. I would trace the electrical circuits from the motor back to find out where the voltage drop is occurring. Then determine why. You should call a technician it will probably cost less to have someone find the true cause instead of guessing.

  36. Chad Hacker

    Hello, I have a Carrier split system. My symptom is the system will kick in, then after about 1 minute there is a loss of power for a split second on both the air handler and outside unit then it kicks back in . The weird thing is after the power loss it seems to blow colder air.

    Reply
    1. thehvacguy Post author

      Sounds like it could be a loose wire in the air handler or a bad float switch in the drain pan. That’s where I would check first.

      Reply
  37. Al weber

    I need to replace a capacitor that is 25 +/- 5. I can’t find anyone e that has one can I use a 30 +/- 5?. The outside fan isnt working, the compressor is working.

    Reply
    1. Al weber

      I need to replace a capacitor that is 25 +/- 5. I can’t find anyone e that has one can I use a 30 +/- 5?. The outside fan isnt working, the compressor is working.

      Reply
      1. thehvacguy Post author

        No that would put the compressor under unnatural loads and cause early compressor failure.

  38. hvac contractors

    I am not sure where you are getting your info, but great topic.
    I needs to spend some time learning much more or understanding more.
    Thanks for excellent information I was looking for this information for my mission.

    Reply
  39. Don

    My A/C inside fan will stop running and fail to restart when the tsat is set to “auto” before the set temp is reached, when this happens the outside fan and compressor continue to run, I have to cycle the main power switch to get it to restart. When set to “on” the fan runs in 2-speed mode, slow when compressor is off high when it’s on.

    I have replaced the outside contactor and delay on break, the inside control board the tstat and the door switch.

    I am thinking maybe the inside fan run capacitor is the last cheap thing.

    It is a 20 year old Ruud Silhouette II gas furnace + Ruud scroll condensor.

    Reply
    1. thehvacguy Post author

      It wouldn’t hurt. That is probably the first thing I would check with those symptoms.

      Reply
    2. Don

      So, the capacitor can cause the blower to stop running? I am having trouble with the logic, but it’s the only thing short of $5000.
      BTW, the reason I started with the contactor is that it was welded closed, after that fix the blower shut down but the compressor & fan continued.

      Reply
  40. Randy

    Hello
    When I set my thermostat to cool, the inside fan blows but the outside fan does not turn on. When I look at the contactor outside I see that it is stuck out. If I press down the contactor with a stick the outside fan turns on but as soon as I let off the pressure the contactor pops back out and the fan turns off. Should I replace the contactor or the capacitor?

    Any help would be appreciated. Thank you

    Reply
    1. thehvacguy Post author

      Neither. It is a low voltage break in the circuit and is doing this as designed. The break could be caused by a loose wire, pressure switch or float switch. Find the root cause where the low voltage is not passing and then resolve that issue.

      Reply
  41. Habib

    Dear Sir

    Our capacitor Carrier Split-type, dual capacitor becomes faulty after about every one week. What is the problem could be the capacitor?

    Regards

    Reply
    1. thehvacguy Post author

      I would look to possible voltage issues in the power to the unit. Also check the contactor to see if it is making solid contact or is it rattling and sparking across the contactor.

      Reply
  42. Russell

    My condenser fan was not running and making a buzz noise every minute or so. i was able to jump start the blade with a stick and is running. The indoor air had been blowing the whole time, it just was not cooling. After a whole night of the condenser fan running the inside air is still not cooling. If I replace the capacitor will it start cooling??

    Reply
    1. thehvacguy Post author

      Possibly. You capacitor appears to be dead and that may mean your compressor is not running. Replacing that capacitor may get the compressor running to move the refrigerant. That may start cooling but you could have other issues that resulted from the bad capacitor.

      Reply
    1. thehvacguy Post author

      Not enough to go on here. One guess or place to start is to check your capacitor. Maybe the compressor is not running due to the capacitor. Another may be the compressor is dead. Just not enough information here to be sure.

      Reply
  43. Jeff Johnson

    Hi there. In the last few weeks, I’ve had the dual capacitor on my Carrier 3.5 T system replaced at the outside unit, and a low voltage fuse at the inside unit fixed because of failure. Obviously, these are two separate items, but I think it’s too coincidental to go unnoticed. System is only 2 years old and we’ve never had any issue until now. To no avail, the techs cannot find any underlying or related issues. Now for the 3rd time in 2 weeks my system is not running and it seems an awful lot like the capacitor again at the outside unit (inside fan turns on, but no outside runs). I’ve checked breakers and nothing is tripped. Any ideas?

    Reply
    1. thehvacguy Post author

      Yes, a good possibility is your system is low on Freon. There is a good chance you have a “low pressure switch” on the refrigerant line inside the outside condenser unit. You should be able to see it from the fan grate. it will look something like this:

      http://www.bestbuyheatingandairconditioning.com/Merchant2/graphics/00000001/Pressure%20Switch%20Low.bmp

      This will prevent the compressor from running if there is not enough freon (which contains the compressor lubricant) so that the compressor does not burn out.

      The two issues you have had are not related and are failing for different reasons. The capacitor is like a battery and has a lifespan meaning it needs replacing every few years. The low voltage fuse means that somewhere along the lines the thermostat wires crossed and shorted out. That could have happened when someone replaced the thermostat or when the technician was testing the control wires for the system when the capacitor went out or if you have had any other service to the system and the technician accidentally touched the thermostat wires to a ground.

      If you do have a low pressure switch, you may have a leak in the system and should get that checked out.

      Reply
    2. "Chico"

      Just as a matter of interest, if nothing is running on the out side unit, while it could be a capacitor either fan cap or compressor cap, out of refrigerant or lack of signal from the controlling circuit could easily be the problem. If a fan cap fails, for a short while the compressor could run if no problem with the refrgeration side, if the compressor cap fails, unless there’s a power faillure, the fan 9outof10, would be running.
      A fan cap is less likely to fail as the load is much less that it is for the compressor.
      A cap on a compressor “gone out of capacitance” can, at times cause the controlling braeker to trip open as a over-loading can be present due to the cap being “out-of-range”
      Cheers.

      Reply
      1. thehvacguy Post author

        Also if the fan cap is out and the fan does not work outside, the compressor will overheat and stop on thermal overload. This is not good for the compressor and significantly affects its useful life. The compressor will turn back on once cooled but the cycle will repeat and the compressor will eventually fail.

  44. Champ

    The circuit breaker that the outdoor unit is tied to continues to trip. When this occurs, the indoor unit continues to run. Within the past week, I have had the experts come out and replace a condenser fan, replace the evaporator coil, and recharge the refrigerant. Any ideas about the reason for the circuit being tripped, I believe it occurs when the unit is trying to kick on. Thanks.

    Reply
    1. thehvacguy Post author

      You have a short in the high voltage. Probably inside the compressor motor. Disconnect the power. remove the wires to the compressor. Check for continuity from each compressor terminal to ground if you get continuity then the compressor has shorted to ground and is basically dead.

      Reply
  45. Michelle salcedo

    The outside fan is blowing and I can hear the unit turn on but no air is coming out the vents. Could it be the capacitor please help thank you

    Reply
    1. thehvacguy Post author

      It is possible, but the indoor blower is tied to many other components and the root cause may be (but not limited to) one of the following:
      1) Blower Motor has failed
      2) blower motor capacitor is dead
      3) fan switch/relay is dead
      4) furnace circuit board is dead
      5) short in the wires
      6) blocked air flow
      You need someone to come diagnose and repair your blower system.

      Reply
  46. cameron

    I have a Goodman split system. When the Tstat is calling for heat or cooling neither indoor or outdoor fans come on. Nothing with FAN ON switch either. I can hear the compressor running when I go outside, and I can also hear the refrigerant being metered through the evaporator. I’m thinking it is unlikely that both blower capacitors went bad. Maybe I’m wrong. Any troubleshooting tips?

    Reply
    1. thehvacguy Post author

      1) Sounds like the outdoor unit is in Defrost mode and you have a heat pump. The outdoor fan not running is normal in defrost mode. Wait about 2 minutes for the system to switch back to heat mode and the outdoor fan should come back on. 2) if you can hear the refrigerant then you may be hearing what they call “flash gas” and it means your system is low and you have a leak. 3) If the indoor fan is not working, then you have a big problem, one that could involve one of the following (a) fan relay, (b) fan motor, (c) capacitor, (d) low voltage shortage, (e) thermostat problem or something else. Hard to say without seeing the unit. call a trained technician, you need some serious work on the system.

      Reply
  47. Hung Nguyen

    Hi. I have an LG reverse cycle AC. When I turn it on the indoor unit works and blows out cool air then slowly the air becomes room temp. The fan on the outdoor unit does not spin and there is no noise coming from the unit. I’ve replaced the capacitor (3 terminals on top) but nothing has changed. Could it be the smaller capacitor (2 terminals on top)? It’s an LG aircon model LS2463HL. I’ve tried manually turning the fan but it still doesn’t turn on. Thank you.

    Reply
    1. thehvacguy Post author

      Hi Hung,
      There are several issues you mention. I’m going to try to repeat them. 1) You have a heat pump. 2) When on the air starts cold and warms up but only a little. 3)The outside unit fan does not run. 4) No noise form outside unit. 5) Spinning the fan blade does not start the fan.

      So here goes: Since you mention a smaller capacitor, it is either you have a big package unit and has a dual capacitor for the compressor and Condensing Fan and has a smaller capacitor for the indoor blower fan. The other possibility is you have a split system but instead of a dual capacitor for the outside unit, someone has put two capacitors in it and is using a single capacitor for the condensing fan. So there is a possibility that the condensing fan is running off the smaller capacitor and it needs changing.

      On the other hand, there is the possibility that your condensing fan is burned out. Since it doesn’t turn even after you try to spin it. I cannot rule that out either.

      Another issue is that the condenser motor is not running, as you mention no noise is coming from the unit. Now if both fan and condenser are not running, I am more inclined to look for a common cause, maybe the contactor is bad or there is no signal to the contactor to pull in the contactor. This can be caused by many different reasons. Some of which include low on freon, short in the low voltage wiring, faulty thermostat. But before you go spending any money on replacing parts, get an expert to check it over so you only have to replace or repair the problem that is causing your unit to not work.

      Good Luck.

      Reply
      1. nate richburg

        AC unit was tripping breaker when it started. I replaced the start capacitor, and now it comes on without tripping breaker. The problem now is that there is arcing on the run capacitor when the unit starts up and when it shuts down. I replaced the start capacitor with the exact same size that came off of it.

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