Posted on 30 Comments

Problem: What to look for when a capacitor is bad? My unit will not do anything!

Bad oval capacitor on the left

Problem: What do I look for when a capacitor is bad? My Air Conditioner unit will not do anything!

Answer: Capacitor problems are probably the second most common problem that I see every summer in our 28 year old HVAC business! Air Conditioning and heat pump systems low on refrigerant charge are the most common problem that I see. Changing out a capacitor is a simple, inexpensive problem that most all homeowners can fix easily if you are good with your hands and have the right capacitor. Weak or bad capacitors can also cause blower motors to not run or to run slow. We have two real good YouTube Videos near the bottom of this page which explains how to replace and troubleshoot an air conditioner’s capacitors.  We sell over 80 different capacitors on the following page: Please click here to see the capacitors we sell.

What to look for when a capacitor is bad:

The Air conditioner outdoor unit will not come on. Either the outdoor fan does not run, the compressor does not run, or both the fan and the compressor do not run. You have checked and reset your circuit breaker. The outdoor unit still does not come on. You can here a little humming sound inside the unit which is the low voltage contactor humming. Please pull the disconnect and disconnect the power to your outdoor air conditioning unit.

*Please make sure your electrical power is off before working on any air conditioning equipment. You take the door or cover off your outdoor unit’s control box and find a bad, swollen run capacitor. EPA stopped allowing manufacturers to produce capacitors with cancer causing PCB’s. Since they stopped allowing the use of PCB’s the capacitors now have a shelf life. Many times I see capacitor problems that will not allow the compressor or the fan to come on. Many times you can clearly see that the capacitor is bad because it is swollen or even blown apart with capacitor oil everywhere! Please see the pictures below.  Sometimes you need a special meter to test the microfarad (MFD) or UF rating. A capacitor tester. Please click here if you are interested in seeing a real good Supco Capacitor tester.

“MFD” and “UF” mean the same thing, “Microfarad”. Many times you will see an “UF” rating on the capacitor instead of “MFD.” Yes, these two abbreviations mean the same. Most of the time you can tell that a capacitor is bad because it will be swollen up. Please see the picture below for the comparison between a good and bad dual run capacitor. We call them dual because the capacitor helps run both the fan and the compressor. If you have any questions please email us anytime or comment below. Our email address is: support@arnoldservice.com

*Tip: When identifying the capacitor that you have, you might see the rating stated in “MFD” or “UF.” “MFD” and “UF” mean microfarad rating and mean the same. Below we have some pictures of bad round and oval capacitors. Sometimes capacitors are weak and need to be replaced. If you do not have a capacitor tester…I would suggest taking the capacitor to an appliance parts supplier and ask them if they would be kind enough to test the capacitor for you. Please click here if you are interested is seeing the over 80 different capacitors we sell. We would love to help you out and have your business!

Bad round dual capacitor on the left.
Bad oval capacitor on the left.

Below we have a real good informative video which shows how to troubleshoot and repair an air conditioner’s contactor and capacitor. Thanks to Kevin Miller for making this informative video!

Below we have a real good informative and educational video on “Dual Capacitor Checkout Procedure” made by Ron Walker. Thanks so much to Mr. Walker for making this informative video!

30 thoughts on “Problem: What to look for when a capacitor is bad? My unit will not do anything!

  1. Hi Steve, my Lennox condenser unit is 3 tons , single phase. 6 years ago Compressor was replaced and running OK , it will cool down stair but hardly cutoff by itself if outside temperature is above 90 degree. Most the time it runs all day and all night even I set 77 degree at thermostat. 2 service man come, after they put the gauge to check pressure of the suction line they sai it is fine, suction line is cool and sweat. However when I show them the warm air comes out on the top of the fan is not warm all over, the air blows out ,one side is warm , another side is cold not cool. After they talked to their manager and told me I need to clean condenser coil, it may block the air flow. Next day I turn off all power and used 2 cans to clean and I can see through to coil . Blow the water out of condenser coil, let it dry about one hour, turn back on: Same thing. Air blows out from the top of the fan; one sit is warm , one side is cold. I notice that the fan start OK, the Compressor starts with some noise for couple second and then runs smooth after that. Do you think it may cause by Capacitor? Please help.
    Thank you very much.

    1. Hi Truong! If you are referring to the outdoor condensing unit blowing one side cold and one side warm then this is quite unusual! Warm out should be blowing out of the outdoor condenser coil all over. You might have some variance in temperature coming out of the top of the condensing unit, but it should never be cold. If this is a heat pump then I would think that you have a reversing valve that is stuck somewhere between heating and cooling mode or you have a bad TXV (thermostatic expansion valve). I do not think that this problem is caused by a capacitor. The compressor would not come on at all or would run and could over-heat if the capacitor was weak or bad. It would not hurt to check the capacitor and make sure it is up to specs, but the capacitor should not be the cause of the cold air coming out of the top of the condenser coil. I have never heard of this except in the wintertime when a heat pump is in heating mode during the winter cold air blows out the top of the unit because the condenser and evaporator trade places during the wintertime. I would suggest that you have a reputable company come out who is a dealer with the brand name equipment that you have. For example, if you have a Carrier unit then I would call a company who is a dealer for Carrier so they are experts with the brand unit you have. Sorry that I can not be much help. I hope you can get this taken care of soon! Steve

      1. Good morning Steve, thanks for fast replying.
        This condenser model HS18-411-5P by Lennox. Compressor was replaced by Copeland # CR34KQ-PFV-980WB. It ran for 5 years OK but not like original. Also new Evaporator was replaced 6 years ago. I checked the condenser fan this morning, the air blow out ; in the means time one side is warm and another half is cool not cold like before, and it never cool the house down to 77 degree. I’m sorry to bother, . I will take your suggestion to call Lennox rep. Thanks again.

      2. Yes, If it is not cooling the house then you have a problem that should be troubleshot by a Lennox professional. Sorry that I can not be much help. Steve

  2. The fan in the compressor unit would not run. I replaced the 35/5 capacitor and it ran great for 4 days. Now the fan will not start again, compressor runs. I bypassed the contactor to see if it may be faulty, but had the same result. The fan rotates freely. Any suggestions? Thanks

    1. Hi Rick! If you are getting 220 to 245 volts AC to the condenser fan motor and it will not work then sounds like you need a new fan motor. If you would like for me to look up the motor your unit uses I will be glad to try. Please send your model number to our email address: arnoldservice@gmail.com and I will try to look it up. If you have a Carrier or Bryant unit I will need the product number. Thanks for asking this question. Steve

    2. I was told by am HVAC tech that my capacitor was bad. I was experiencing all the indicators that it was. I got the new capacitor and connected it. There were two differences from the old capacitor: the new one is metal and it had a dent in it. The vendor said it was damaged in shipment and gave it to me for free. Also said they tested it and it was fine. So after everything has been installed and connected properly, when I try to turn the inside breaker on, it automatically pops back off immediately. I have checked and double checked all connections. Did I do something wrong?

      1. Hi! This sounds like you have a direct short to ground somewhere in the system. This could be that the capacitor is wired wrong or that your compressor has grounded out and you need a new compressor. On the capacitor, there are 3 connections COM, which is the power coming into the capacitor usually from the contactor. Fan goes to your fan motor and Herm goes to the S Start winding of your compressor. If these are not hooked up properly it could cause the breaker to trip. If you want to make sure your compressor is OK then you will need to turn off the power and ohm the 3 connections out on the compressor. We have a post on how to test your compressor on the following page: https://arnoldservice.com/problem-i-installed-the-new-capacitor-and-the-boost-cap-i-received-now-the-outdoor-fan-will-start-briefly-but-the-compressor-does-not-the-power-management-box-on-the-side-of-the-house-shuts-off-pow/ We also have another post that might help you out: https://arnoldservice.com/problem-my-air-conditioning-unit-blows-the-circuit-breaker-after-it-runs-for-a-while-what-could-be-the-problem-would-a-super-boost-compressor-hard-start-booster-help/ I hope you can easily find and fix the problem without needing a new system. God bless you and your family. I know it is hot most everywhere! We have a 105-degree heat index here in Louisville, KY! Steve

      2. Hi Steve. God bless you and yours as well. Yes, we are experiencing record temps here in Georgia too. It doesn’t help that I have high blood pressure in this heat. I am trying to save myself some money by figuring this out myself. I have the diagram of the unit which was inside the panel there are 3 wires: red, brown, and blue. According to diagram, brown is for the fan, blue is the herm and red is C. I haven’t screwed the panel cover back on. Do you think that could be it? I mean, if it were off with power flowing through it, it does pose a risk for shock. I am going to put the cover back on and see if it makes a difference. Thank you for all of the advice and information. 🙂

      3. Hi Mr. Sims! Thank you so very much for your blessings! Yes, the wiring diagram sounds right with red being the power wire that is connected to C, blue to the herm and brown to the fan motor. I would strongly recommend that you get a cheap voltmeter at Home Depot or Lowes if you do not have one. One side of the breaker could still be on and it could give you a shock. If the breaker will not reset then you have either a direct short to ground somewhere or a bad breaker. You, an electrician or an HVAC check should check out the voltage with a meter making sure you do not ground yourself out and get shocked. I would recommend turning the power off and disconnecting two of the wires that go to the compressor to see if the breaker will stay on with those two wires disconnected. If the breaker stays on with the two wires disconnected that go to the compressor then this is a sure sign that the compressor is grounded out and you either have a burnt wire on the compressor terminal block or the windings are shorted out inside the compressor and you need a new compressor. If you want to check your power going into the contactor then you should have 220 to 245 volts AC between L1 and L2 on the contactor and with the contactor energized (thermostat calling for cooling) you should have 220 to 245 volts between T1 and T2 on the contactor. It might be best if you have any more questions to email me at arnoldservice@gmail.com. We are going to 5 PM church this evening. I will pray for you. If the compressor is dead then you might consider getting a portable AC or spend the night in a hotel. This heat is not good for the blood pressure as you know. Steve

  3. A contractor serviced my unit and left the new capacitor in the box it came inside my AC unit. The box pushed the leads of the capacitor against the side of my unit which tripped the breaker. I fixed the problem and removed the box (which was also soaked). The next time I had the same company out they said that it was a common practice to leave the box in the unit with the capacitor inside it. Is this common practice?

    1. Hi Jeff! No sir, it is not common practice to leave a capacitor in a box and install it inside the unit. The company should have secured the capacitor inside your unit’s control panel with metal strap or plumber’s strap so that it will not move around and short out. Some times I would tape the capacitor’s connections so they could not ground against the body of the unit. I think I would look for another service company the next time. This is not good work and it could have damaged your unit seriously. Thanks for asking this question. God bless you and your family. Steve

  4. Hi Steve I have a carrier central air conditioner and when I turn it on it just hums and cooling fan motor on the top is very hot to the touch on the surface but that might be because I had it on for a while and didn’t know it wasn’t running properly just humming. I removed the capacitor I don’t have a test meter but there is no bulge on the top to indicate a bad capacitor but I suspect that’s the problem. Do bad capacitors always have to have a bulge on the top as mine doesn’t seem to have that. I ordered one but I’m just wondering what your thoughts are. My air conditioner is only about 5 years old and it wasn’t used very heavily each season and I had it covered when it wasn’t in use.

    1. Hi Joe! This sounds like you either have a bad, weak capacitor or you need a new motor. If you have a capacitor tester I would suggest testing the capacitor to make sure it is up to specs. Yes, capacitors can be weak and not be swollen up. If you want me to look up your unit’s motor part number then please send me your unit’s product number to our email address: arnoldservice@gmail.com If your unit’s motor was not running for a while then the compressor has probably over-heated and gone off on thermal overload. It sometimes takes over-night for compressors to cool down and reset the thermal overload. I hope you have a happy 4th of July! Steve

  5. Hello, Mike here , my unit quit working, it is 4 years Old, it is a carrier brand, would the capacitor gause my condensation pump to stop working, and what would a new capacitor cost, as well as the other piece installed in your video.
    Thank you Sincerely, for any and all help.
    Mike.
    Email: mikeolddog1@ yahoo.com

    1. Hi Mike! Yes, the capacitor could cause the unit not to work. You would need to do some troubleshooting to find out what the problem is. It could be any one of many problems that could cause your air conditioners to not work. If you do not have a volt meter I would like to suggest that you get one so you can test to see where the problem is located. We have an air conditioner troubleshooting flow chart that I hope will help you determine where the problem is: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  6. I replaced my capacitor and fan and compressor still isnt working!! What else could i check? Its getting 240 to the unit but nothing works not even a click!

    1. Hi Robert! It could be any one of many problems that could cause your air conditioner to not work. Is the contactor closing when your thermostat is calling for cooling. If not you could have an open low-pressure switch or a thermostat problem. If you do not have a volt meter I would like to suggest that you get one so you can test to see where the problem is located. We have an air conditioner troubleshooting flow chart that I hope will help you determine where the problem is: https://arnoldservice.com/wp-content/uploads/2014/12/air-conditioner-troubleshooting1.pdf We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  7. I am looking to replace my dual run capacitor. My heat pump is working fine but I am about to add a 5-2-1 Hard Start (3 wire) capacitor in hopes that my generator will start the A/C unit during power outages.

    While prepping for the install, I removed the Dual Run Capacitor and checked it. Both sides were falling slightly below the tolerances printed on the label so I ordered a replacement with the same specifications.

    The new capacitor is 45/5/440R +-3%. When I test the HERM side I get 47.35MFD which is more than 3% higher than the tolerance. Should I return it or is this close enough?

    1. Hi Rick! I would not return it because most of the time capacitors lose their capacitance value over time and since the capacitor that you have is slightly over it should be good for a long time. Thanks for asking this question.
      Steve

  8. I am getting a Status Code 41 on my t-stat which is, motor control has detected that the motor will not come up to speed within 30 seconds of being commanded to run or that the motor has been slowed to below 250 rpm for more than 10 seconds after coming up to speed. My capacitor is testing a bit low and not within the 6%. I was getting 4.2 out of 5uf. The other side of the dual capacitor was giving me the full 35uf. Could my capacitor be the cause of this?

    1. Hi Jonathan! I am sorry that I am not familiar with a system that sends the status codes through the thermostat. You must have a pretty high efficient system with lots of electronics. Sorry I have not been doing any service work since 2005. I would think, in what little I know that the code would be referring to the blower motor on your furnace or air handler. If the code is coming from the outdoor unit then yes, I would suggest replacing the dual run capacitor on the unit because 4.2 uf is a little low and it could affect the speed of the outdoor fan motor. I always heard that a capacitor should be within + or minus 10% and 4.2 is below 10% of 5uf. So I would recommend replacing the capacitor. Sorry that I can not give you much help. Steve

  9. Can u replace a 45+10 with a 45+5

    1. No sir, you can not replace a 45/10 with a 45/5 capacitor. The fan would not work properly and probably would not work at all. The voltage is important too. You can always go up in voltage, but never down. For example if you have a 45/10 mfd 440 volt capacitor you need to replace it with a 440 volt capacitor, not a 370 volt capacitor. If you have a 370 volt capacitor you can go up to a 440 volt capacitor. I hope you have a great day!
      Steve

  10. At the very top when you said “Weak or bad capacitors can also cause blower motors to not run or to run slow”. Did you mean condenser fan instead of blower motor? Just curious, because my condenser fan is only running about 20% as fast as it should and the compressor is grinding as it fails to start. Tested the cap and it was ok, but I only have an analog meter.

    1. Hi Carl! Weak or bad capacitors can cause both blower motors and condenser fan motors to run slow. If your condenser fan motor is running slow it could be a weak capacitor or a condenser fan motor where the bearings are dragging and the motor is on its way out. You will need a capacitor tester to test capacitors. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ I hope you have a great day! I hope you can easily find and fix the problem. Steve

  11. can you replace a 40/5 uf 440 vac capacitor with a 45/5uf 440 vac capacitor.

    1. Hi David!
      I would not recommend doing this because manufacturer’s recommend plus or minus 10% 10 percent of 40 of course would be 4 uf and you are asking about 5 uf difference so I would not recommend this. I would recommend the exact replacement because compressors are too expensive to take chances. Steve

  12. My unit has a single capacitor. My local HVAC parts dealer does not have the single, but has a Dual unit and they say I can use that. The one I need is a 43/370. The one they gave me is a 45/3/370. They say not to use the 3. I have the new capacitor and it is labeled C, FAN, Hxxx (hard to make out). First can I use this capacitor? and what wires go to what. Your description above for the Dual says the 3 is for the fan. This is why I am confused, I think my fan unit is bad. They say use the 45/370, but the capacitor has FAN on it but your website says that is the 3uf. Please clarify…..

    1. Hi Andrew! Did you watch the Youtube videos that are on our page: https://arnoldservice.com/capacitors/. They should explain. Yes, you can use a dual capacitor to replace a single capacitor. The capacitor that you want replaced I think from your description is the 43 MFD/uf 370 volt single capacitor. Yes, your service people could use the 45/3 MFD/uf 370 volt capacitor as a replacement since the 45 is not 10% more than the 43 that you want. This capacitor is for the compressor only and you should only use the “Herm” and “Com” terminals on the capacitor. The “Herm” connection wire would go to the start terminal on the compressor and the C (com) wire would go to a power source usually from the contactor. You would not use the “Fan” terminal on the capacitor because as far as I understand the capacitor is not being used for the fan only for the compressor. You probably have another capacitor the fan is using. I hope you can easily fix your air conditioner or heat pump. Steve

Leave a Reply

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