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What Is a Compressor Capacitor?

By Amy Rodriguez
Updated May 17, 2024
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A compressor capacitor is an electronic component that attaches to an air conditioning system's compressor unit. It stores and releases electrical energy to run the compressor at the initial start up and during operation. In fact, there are two types, including start and run versions.

This specialized electronic component normally resembles a small cylinder with positive and negative terminals protruding from one end. The compressor capacitor attaches directly to the compressor's electrical supply. Energy within the capacitor maintains the compressor and fan motor speed at a consistent power level. As a result, the compressor and fan have long lifespans.

Start capacitors provide the extra energy needed when the compressor unit activates during the air conditioning cycle. The compressor's motor requires an initial torque boost from the capacitor's stored energy, effectively beginning the compressor's operation. After the compressor capacitor provides the starting energy, it disengages from the compressor unit. This disengagement action allows the run capacitor to engage with the electrical system. A start compressor capacitor will store some of the running electricity within its assembly for future start-up torque power.

Run capacitors maintain a steady electrical power supply to the compressor during operation. Electrical power can vary in voltage over time, which can harm a device's circuitry. In response, the design of the run capacitor requires it to be located between the power source and the compressor unit. Electrical power is reserved within the capacitor; the compressor draws the needed power from the capacitor, providing a safe and constant electrical flow.

Over time, a compressor capacitor can fail. Most compressors are located outside since they can be relatively loud during operation. As a result, these electronic components are prone to failure because of old age or weathering the elements. An air conditioning system that fails to activate may indicate a bad capacitor. Alternatively, the compressor and fan may not activate while the inside components try to operate.

A bad capacitor can look enlarged or even dented. Many homeowners replace the capacitor on their own, although care must be taken in doing so. All electrical power must be removed from the air conditioning system to prevent accidental electrocution. The repair person should note the colored wiring attached to each capacitor terminal for correct attachment to the new component.

A new compressor capacitor should have the same power rating as the old capacitor. The new capacitor can have a higher power rating than the original component; however, lower power ratings should not be used. Pairing a capacitor with less power than the original with the older compressor may damage the equipment, resulting in costly repairs.

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