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Kilowatt Heating, Air Conditioning and Electrical Blog

Understanding Capacitors and Contactors: Essential Air Conditioning Parts


Air conditioning systems are often called refrigerant-based systems because they use the circulation of refrigerant to move heat from inside a building to the outside. But air conditioners don’t actually run off the refrigerant: they’re electrical devices that take the power to run their components from the electrical system in a building. They’re complex electrical devices as well, and the majority of malfunctions an air conditioner can encounter happen because of electrical problems.

We’d like to focus on two electrical components in your AC that are essential for it to work: the capacitors and the contactors. These parts work together to allow the motors in the air conditioner to run—and they will both eventually wear out, fail, and need replacement. It’s best to think of them as temporary parts. Regular AC maintenance will help technicians catch dying capacitors and contactors early, but you may find yourself caught off-guard and need AC repair in West Hollywood, CA.

The Capacitors

Capacitors are like temporary batteries: they hold an electric charge and then send it to a motor to either start the motor running (a start capacitor) or to keep it running (a run capacitor). The motors for the compressor and the fans must have capacitors in order to work.

Capacitors will run down and start to lose their ability to hold a charge over time. High heat levels also contribute to shortening a capacitor’s life. As a capacitor starts to fail, it will give off a clicking noise. Should the capacitor fail entirely, you’ll only hear a hum from the motor when it starts. Don’t continue to try to run the motor in this case, because it can burn out! Call for technicians to put in a new capacitor.

We’ve included a picture at the top of Byron showing a rusted bad capacitor on the left, a good new capacitor in the middle, and a bulging bad capacitor on the outside.

The Contactors

A contactor is an “on/off” switch to the compressor and condenser fan. It controls whether voltage moves toward these components and therefore whether the AC is on or off. When a contractor fails, you may find that the air conditioning’s compressor won’t turn off at all, no matter how you adjust the thermostat. Debris and dust getting into a contactor can also cause it to fail.

Let the Professionals Work With These Parts

Please don’t try to go DIY with replacing either capacitors or contactors. It may sound like a straight forward job to swap out old for new—after all, you can purchase both online—but it isn’t. You put yourself at risk of a dangerously high voltage shock when you try to change these components on your own. Call our HVAC professionals so you’ll stay safe. We also strongly recommend signing up for our regular maintenance service. A simple inspection for your air conditioner each spring goes a long way toward preventing emergencies from failed electrical parts.

Kilowatt Heating, Air Conditioning, and Electrical has served Los Angeles, Van Nuys, and the San Fernando Valley since 1990. Schedule air conditioning service today.

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