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

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829 thoughts on “Common Air Conditioner Capacitor Failure Symptoms”

  1. My ac cools fine but when it first starts the outside unit makes a loud buzzing noise like a bugszapper . It does it about every ten seconds for about a second and then it does it about every 20 seconds for a fraction for the next 5 or 10 minutes and then about every 5. Minutes after that it buzzes for about 10 seconds. Fan motor is spinning all the time. Large pipe next. to freon line is sweating and dripping slightly. Rheem 5 ton unit

  2. I have a 2 ton unit. Works fine for heat and cooling. However, when the unit has been used for heat – we live in FL had it on a few days – then today it was 77/78 out. I went to turn it from heat to cooling and the compressor did not start. This was well past the “cooling on” blinking indicator for the delay. I was reminded this happened in the past and we wait a few hours and turned it on again this time from “off” and it worked fine and again starts daily with no issue when on cooling.

    Can the capacitor be an issue?

  3. Outside unit will come on only after breaker is turned off then back on. Then it shuts off after about ten minutes. Thermostat flashes “heat on” then auxiliary heat comes on after a while. Outside unit seems normal while working just won’t work all the time. Replaced the capacitor on the outside of the unit and the contactor last year. Could the capacitor be bad again?

    1. It could be, but I would really need to put some tools onto the equipment to check pressures and voltages to see what is happening.

  4. My 2 ton, 10 SEER Rheem Classic heat pump (approximately 11 years old) is tripping the circuit breaker. The thermostat will call for heat and air handler turns on, but the outdoor unit will not. I will sometimes hear a “click” outside when the unit should have kicked on. I had a technician out earlier this year when it was doing the same thing. He replaced the capacitor and the circuit breaker and it resolved the tripping issue. When I reset the tripped breaker, the unit will turn on. It usually makes it through one or two cycles before tripping the breaker again. On occasion, it gets caught in defrost mode. I turn the system off at the thermostat, wait 10 minutes and turn it back on and it resolves itself until it trips again. I had the defrost board replaced last winter. The capacitor does not visibly appear that it has failed, but I have not tested it with a multimeter. I do not observe any loose or burnt out wiring. Any thoughts? Thanks.

    1. The breaker will trip in overload conditions. This is when the unit tries to draw too many amps. Typically this is when it starts up and is a sign the motors are going bad. If the motor bearings are worn, then it draws a lot of current to try to get the motor to rotate, thus tripping the breaker. In this case the compressor may be going bad.

      Another reason breakers trip is because of short circuits. That can be a bad capacitor, loose wire, bad heat strips, or other situation where wires may be crossed.

  5. My LG neoplasma split will only run for about 10 seconds before the outdoor unit stops working. The indoor unit continues working but the fan icon on the electronic display disappears and the outdoor unit stops working. after about 1 minute, the fan icon on the indoor unit comes on and the outdoor unit runs again for about 10 seconds before shutting off. this is repeated over and over again. There is no cooling effect and no water coming out of the drainage pipe. When I disconnect the powerline to the outdoor system, the indoor unit tends to work properly with the fan icon on and the fan blowing for as longs as the system is on. Hope that I don’t have a big problem on my hands?

    1. It sounds like you have a serious problem but the information is not enough to provide you with any kind of valid diagnosis. You had better call a professional to put some test equipment on the unit to find the problem.

  6. I have an old carrier heatpump with a Positive Temperature Coefficient Resistor start circuit (like made with a ceramic case) that was replaced with a supco super boost spp6 ptc years ago. Now it is hard to start the compressor again. Should I replace this hard start capacitor with a 3 wire version (ie 521) or would the torque be too much for an old heat pump (over 35 years old)?

  7. have a walk-in cooler that needs to be about 35F. The compressor everything seems to be ok until unit runs for about 30 minutes. the amps get a little high(rla is 10.6, unit slowly as txv opens/closes, increases up to about 14/15amps) then all of a sudden it acts like it is trying to stat all over again and the amps spike up to 40+.(trips breaker) Let it cool some and the time lessens but same issue. Could it be the run capacitor. I checked it originally and it was 20.1 for a 20 microfarad part. I changed the start capacitor as it was reading way high(145-174, reading mid 190’s). The box is starting out warm at 70/72F. Can a run capacitor appear fine but fail under load causing this issue? My mind says yes. Thanks!

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