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Common Air Conditioner Capacitor Failure Symptoms

December 11, 2012

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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121 Comments
  1. Michelle salcedo permalink

    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

    • thehvacguy permalink

      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.

  2. cameron permalink

    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?

    • thehvacguy permalink

      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.

  3. Hung Nguyen permalink

    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.

    • thehvacguy permalink

      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.

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