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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475 thoughts on “Common Air Conditioner Capacitor Failure Symptoms

  1. alex

    hi i have a rheem seer 10.there seems to be a box where the electricity goes in that has a slot for a flat metal piece with a plastic grip handle.Its missing but it was there at one point and its needed to have power to go to the ac unit outside..anyone know what this is and if i can get a replacement. thanx

    Reply
  2. Josh

    Fan on outdoor unit was not spinning while blowing warm air threw vents on inside of home. Changed capacitor, it was obviously bad. Of course I turned breaker off before changing capacitor but did not turn power off to furnace inside. It’s a older unit with a dial thermostat. Ac worked fine after installing new capacitor but when it reaches desired temp does not seem to shut off. If I turn the temp on the dial above room temperature I do not here the click on the dial but it does shut off minutes later. Do I have a problem here? Did check the fuse on the panel on the inside furnace. Not blown. Is it the transformer?

    Reply
    1. thehvacguy Post author

      I got a mixed signal from you. Does it shut off or does it not shut off? A delay shutting off is normal in certain conditions. Typically if the unit only minutes before was turned on, the delay is to prevent short cycling.

      Check out our web site for other articles and videos.
      http://www.alexhvac.com

      Reply
  3. Rob

    Hello HVAC Guy – some great information here. My scenario is as follows: 2.5 ton Kenmore Unit – a little over 10 years old. A few weeks ago the unit started intermittent cooling. First thought was to replace fan capacitor – done. Worked for a few days – then fan ran intermittently such that the compressor would shut down – again no cooling. Replaced the fan motor – cooling and compression ok. After five days – no cooling but fan runs properly. Freon levels are ok. Other thoughts – bad capacitor for compressor, bad relay or compressor is toast from too many over heat cycles. Most frustrating part, the unit was 37 days outside warranty when it failed – Sears not helpful :( Any thoughts on the next steps? Replace compressor capacitor, replace relay, replace compressor/entire outdoor unit? Any thoughts would be appreciated. Thanks very much :)

    Reply
  4. joe

    Hi HVAC Guy,
    So today I came home from work and noticed my air wasn’t blowing cold and the ac unit outside was not spinning after a little research I tried the “stick trick” and the motor started to spin freely. And as of right now the motor is still going strong only problem now is the ac is still not blowing cold out of the vents. Im hoping its just a bad capacitor. Thanks in advance for any help you can offer.

    Reply
  5. Casandra

    AC cooling, but fan outside spins for a minute or so then stops & starts buzzing. Just got back from vacation & not what we were looking forward to coming home & seeing. ..

    Reply
    1. thehvacguy Post author

      Yes it can be a real headache when this happens. Sorry to hear it happened right after your vacation.

      Reply
  6. Hot in Mississippi

    Hello, first I want to say that I’m amazed by your response rate. Incredible. I have a question. Can a bad indoor fan motor capacitor cause the fan motor to stop turning when its operational? Thank you.

    Reply
  7. Hot in Mississippi

    Hello, first I want to say that I’m amazed by your response rate. Incredible. I have a question. Can a bad indoor fan motor capacitor cause the fan motor to stop turning when its operational?

    Reply
    1. thehvacguy Post author

      Absolutely. And a weak capacitor can ruin a good fan motor. Having a properly rated and operational capacitor prevents early motor wear as well as creating the best operating conditions for the internal magnets.

      Check out our web site for other articles and videos.
      http://www.alexhvac.com

      Reply
  8. Jason The Hobbyist

    Rain was getting in the control section of our 5-year old Luxaire 3 ton. The dual cap terminals must have got wet several times over the years and the compressor terminal overheated and the wire melted off the connector. I was going to reconnect to the existing cap’s spade with a new terminal but noticed the plastic insulator melted, causing the terminal to look like it may be fairly close to shorting against the cap case. Instead of screwing with it and causing any other issues I replaced the dual 45+5 cap (with two separate ones as my match was not available, of course). Powered everything up fine and been running for 3 hours but as I went to put the cover back on noticed a sizzling sound coming from the compressor cap (the 45uf). It is cool to the touch and so are the leads. Is this normal for a brand new cap? Will it settle in and stop worrying about it? Could also be the contactor but I don’t think so as the noise is more of an arcing/sizzling sound rather than a 60 cycle buzz.

    ¤¤ Amazes me some units run on rooftops for 30 years, but not mine lol. Next time I’ll buy a Carrier. ¤¤

    Reply
    1. thehvacguy Post author

      No, sizzling is not normal. However, is the noise possibly coming from the contactor? sometimes they hum or rattle a bit. If the sizzling is coming from the capacitor, I would probably recommend replacing the wiring where possible as the wires may have been damaged from the previous incident.

      Reply
  9. Pavel

    Hello, great blog. Quick question if you don’t mind. My inside blower motor stops working 3 times a season. I replace 7.5 mF running capacitor and it works again. The motor is 16 years old and started to have this problem about 4 years ago. I assume eventually the motor will go but do you know how long can it last like this? The blower locations doesn’t make it possible to replace the motor without breaking Sheetrock walls and the ceiling. Thank you in advance.

    Reply
    1. thehvacguy Post author

      You’re lucky it lasted as long as it did. The mechanical code in the US requires a level working space of 30in x 30 in in front of the control side to service an appliance. Rooms containing an appliance shall be provided with a door and an unobstructed passageway measuring not less than 36in wide and 80 in high, or large enough to fit the largest appliance in the space.

      From this reading, it sounds like your installation is in violation of the mechanical code in my state.

      Check out our web site for other articles and videos.
      http://www.alexhvac.com

      Reply
      1. Pavel

        Thank you for the quick response. It is what it is, when you are a first time home buyer, you miss a lot of things. Also, I guess I will get a split system when this one dies. The current one is still using freon which can’t be replaced anyway. Thanks again.

      2. thehvacguy Post author

        Freon is a Brand name and not actually tied to one particular formulation of refrigerant. They all use refrigerant (commonly referred to as Freon). They are just changing from R22 to R410 formulation. We are still adding R22 to older units but the prices are rising as supplies decrease.

  10. Mary

    Thank you for this blog! My question is about compresor capacitor install. Ours was replaced but the odd thing is that the technician insisted on connecting it outside the unit instead of opening it up and removing the old one. So it sits in the panel area and works. Embarassed to ask, but was this a mistake, should I have them install it “properly”?
    Thank you

    Reply
    1. thehvacguy Post author

      Just to be clear,, if it is outside the unit, and people are able to touch it without removing a cover or guard, call the cops on this guy. The capacitor is HIGH VOLTAGE and should be protected from accidental contact. If it is covered and behind a panel that must be unscrewed, then it is OK, but poor judgement by leaving the old one there.

      Reply
      1. thehvacguy Post author

        Don’t really call the cops. Call the company owner and if he doesn’t fix it, then call the licensing board and file a formal complaint.

      2. Mary

        Yes poor judgement indeed. In our haste I agreed, fortunately it is covered. However I am going to request they return and install it properly

  11. Julie

    Hi – we have a Lennox unit & it was making a horrible noise (roof mount)- the fan was not spinning is we replaced the capacitor. It’s now working just fine except now it vibrates. It’s quiet outside near the unit but in the bedroom below the unit, there is a loud vibrating sound. There was some play in the fan (going up & down)- could this be part of the vibration problem? Or can you think of another reason?

    Reply
    1. thehvacguy Post author

      It could be that the fan is now out of balance or someone left a screw out when the unit was last checked and the rattling is because something is no longer secured. The play in the fan is an indication the bearings are bad. This can happen when running on a bad capacitor for too long.

      Reply
  12. Fadi

    Hello.. my home AC was working properly this morning. The very same day at evening i turned it on and there was no cool air blowing.. just normal air
    The compressor seems to work normally and so the compressor fan (outdoor unit) also spinning flawlessly but it blows normal air (i think it must be hot) , all working as before but there is no cool air at all.
    I’m confused because a Freon leakage can not be developed in just several hours
    plus if the run capacitor is bad then why the compressor is running ?
    when i despaired .. i removed the plastic cap that housing the wiring on the outer unit so i can see the run capacitor , it was way way hot (the body of the capacitor) with a light burning smell . i stopped at this point and i think that i need a pro person to look into this problem.
    a side notice may be useful :Now when switching on the AC i hear a hissing noise from internal unit that lasts for about 10 seconds and then goes away , i thought it is normal cause i used to hear the same sound every time i switch the AC on when it used to cool very well ,but the hissing sound was taking about like 3 seconds or so (lesser time than it after the problem occurred)
    any thoughts ?
    .
    Thanks HVAC for hearing us
    PS: sorry for grammatical faults .

    Reply
    1. thehvacguy Post author

      A couple of things come to mind. The hissing noise usually is flash gas and is a sign that the compressor is running and you are low on freon. The hot capacitor is due to the location, function and high voltage running through it. It can also be going bad. That might explain why the unit is not blowing cold air all the time as it may not always keep the compressor running. The capacitor should be checked and replaced if weak because it will ruin your compressor. The leak you have may have grown by now and yes it can leak out fast enough to prevent you from feeling cool air. This now sounds like you will need to replace either the coil or the whole AC. I would lean to the whole unit since your compressor may have been negatively impacted by the low freon and the bad capacitor. If you replace the coil, you may find you need a new compressor within the next year if not sooner. Those two independent repairs will cost you almost the same as a new system but without any decent warranty. An annual maintenance program may have prevented this untimely problem. I always recommend an annual maintenance program to be sure the system is in its best conditions and improves the odds for a long life.

      Reply
      1. Fadi

        Thanks for responding.
        My AC unit is just one year old and sadly it is not under warranty. I’m sad to hear that I might need to replace the coil or the whole unit .
        cause the problem happened all of sudden and now i still can see/hear all the components running but the ac is not cooling at all . no frost on the pipes nor the evaporator and the pipes are not cold as it should be.

      2. Fadi

        Update :
        Had the unit checked by a technician .firstly he said it is completely out of Freon. charged it and immediately a resonable hissing sound came from the condenser, the area where the compressor located. He uninstalled the unit a took it to his workshop for investigation. Now it is confirmed that a sudden leakage took place , maybe due to weak pipes conjunction or so ?? . I hope that it is not the compressor.
        Thank you very much .

      3. Fadi

        Update 2 :
        Got it fixed !
        So a tiny pipe inside the unit come into contact with the compressor leg which due to vibration eroded with time and finally cracked ,That explains why the unit lost its refrigerant so fast. Thank you very much and have a cool day.

  13. Wilson Ziegenbein

    I changed out the fan delay relay board and the system again runs like its supposed to! Thank you for pointing me back to the boards to take a closer look. That brown toasty spot was way up on the top edge against the top of the control/wiring area compartment.

    Reply
  14. LG

    My AC unit got hit by power surge from lightning
    about 2 weeks ago, I have been without AC since with 90 degree temps my great ins company sent their expert out saying the capacitor blew and can be replaced

    My AC guy says replace the unit due to possible
    issues of other parts that may come up in a week
    month or so my unit was working fine before
    hit by lightning no repair company wants to touch
    it and be responsible for other parts that may
    go bad

    What are your thoughts?

    Reply
    1. thehvacguy Post author

      I would be upfront with you and give you your options. 1) You can replace the capacitor and see if that holds up for a while but be warned that there could be other damage and I would not warranty anything other than the part for 30 days. 2) Replace the system due to the possible unforeseen issues.
      But here’s your call, pay $150 to replace the capacitor or $5000 to replace the system. It seems obvious to me that the risk of $150 repair and it working, outweighs the $5000 repair that may not have been necessary. This is a decision only you can make. We can only offer the options.

      Reply
      1. LG

        My AC unit got hit by power surge from lightning
        about 2 weeks ago, I have been without AC since with 90 degree temps my great ins company sent their expert out saying the capacitor blew and can be replaced

        My AC guy says replace the unit due to possible
        issues of other parts that may come up in a week
        month or so my unit was working fine before
        hit by lightning no repair company wants to touch
        it and be responsible for other parts that may
        go bad

        What are your thoughts?

  15. Adam R

    Hi, I have a roof top packaged air/heat unit. The air comes out cold, but not very strong. So, it takes forever or never to bring down the house temperature and shut off. Could this be a problem with inside blower/fan? Bad capacitor? Thank you.

    Reply
    1. thehvacguy Post author

      Sounds like an air flow issue. Either your filters are clogged, ducts are crushed, or the system is low on freon (frozen coil).

      Reply
  16. Becky

    So I just had a general maintenance done on my home ac on Wednesday and then on Friday my ac went out. I called the company that did the service earlier in the week but they wouldnt come until monday. I called another company and they came out that day and it turns out the capacitor needed replacing. Is that something the guy should have seen 2 days earlier or do they really go out that quickly?

    Reply
    1. thehvacguy Post author

      Probably but not for sure. It the capacitor blew due to defect and/or high heat, then no. If the capacitor was below specification then yes the tech should have seen that. But it doesn’t always show bad right before it has an internal catastrophic failure.

      Reply
  17. Louie

    Hi hvac guy,

    I have a small trane condenser and the fan kicks on and everything is cooling. Within 5 min. The fan shuts down. Checked the barings and replaced the dual cap. Checked the filters. And the condenser still runs. Plz help.

    Reply
    1. thehvacguy Post author

      I am assuming the fan that shuts down is the outside condenser fan. Sounds like one of three things, bad capacitor, bad fan, or loose wire connection. If its a heat pump, then there is a chance you have a bad defrost board.

      Reply
  18. Wilson Ziegenbein

    We have been living with an intermittent shut down on the air handler for an American Standard package unit. First, during the winter we found that the blower would shut down and not restart in the auto mode. Going to always run, got us through the winter. Now that we have gotten to cooling season the blower is shutting down randomly even in always run mode. When it shuts down, the compressor and coil fan continue to run and the thermostat indicates ‘cool on’. If we turn off both breakers feeding the unit, wait a couple minutes, and turn them back on the blower comes back on, compressor follows and all is good. If it is really hot out it will stay running longer (days) before the blower shuts down, and when moderate temps(80) the time seems shorter (2 hours). There was obvious arcing going on at the main contactor, we changed that. Indoor thermostat was changed to rule that out. We had a tech come out before I started changing anything, he looked at the blower, it restarted when he just physically touched the outside of the casing, charged $75 and left. Would a bad capacitor cause this kind of fault? Or maybe a relay that won’t stay pulled in? Any ideas would be appreciated.

    Reply
    1. thehvacguy Post author

      Well this one is always tricky and would need someone to test all the circuits to find the one that is causing the problem. I would say it is either a loose wire connection or a bad circuit board. Good luck.

      Reply
      1. Wilson Ziegenbein

        So I took another look under the hood after work today…the time delay board is a nice white pcb…except for the area where it is brown around the area where R2 is…think maybe I found the problem with one or more components on that board getting a little toasty?

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