Common Air Conditioner Capacitor Failure Symptoms

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

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

Why do capacitors go bad

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

Diagnosing a bad capacitor

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

For Quick, Honest and Affordable Service, call

Alexander Heating and Air Conditioning

1-919-886-HVAC (4822)

Raleigh Air Conditioner Repair

Holly Springs Air Conditioner Repair

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435 thoughts on “Common Air Conditioner Capacitor Failure Symptoms

  1. 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.

    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).

  2. 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?

    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.

  3. 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.

    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.

  4. 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.

    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.

      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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