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Common A/C Capacitor Failure Symptoms

Posted on The Cooler Blog September 20, 2013 by Terry Jones

Capacitor failure symptoms are harder to identify without the proper tools and expertise. There may be one or multiple capacitors in your A/C. While the most popular capacitors are the types found on circuit boards, the ones associated with air conditioning will be the bigger capacitors that start and run your motors. There are several motors present in an air conditioner and heater systems:

  1. Compressor Motor Run Capacitor – the most popular capacitor that fails. Frequently, these are duel capacitors, which mean 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. Outdoor Fan Motor Run Capacitor – the smaller capacitor that’s 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 – like 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, but these are less common.

Capacitors either go out entirely or gradually. 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. If the capacitor starts to fail, the capacitance measured will be outside of the labeled range. There is a risk of severe shock, so do not try this to troubleshoot yourself at home.

If a capacitor goes out completely, or is severely out of its operating range, it may prevent the motor 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 will short cycle or stop functioning. If the indoor fan stops, then no air flow will pass through the vents.

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