How to Test a Heat Pump Capacitor

A heat pump capacitor is used to give the pump motor an electrical "boost" when a working load is placed on the unit. Over time, the capacitor can become weak and ineffective for delivering that boost to the heat pump motor. This failure can cause the heat pump to work harder and cost more in electricity to operate.

  1. Remove the electrical connections from the capacitor by using the needle-nose pliers. Withdraw the capacitor from the heat pump unit. Place the capacitor on a tabletop for easy access as you may need both hands to perform the following tests.

  2. Discharge the capacitor by turning the meter to the "volt" position on the selector switch and touching the red and black probe ends of the meter to the capacitors bare metal electrical connectors. The voltage may have some type of reading, but will dissipate as you keep touching the meters probes to the capacitors connectors.

  3. Test the capacitor using the digital meter by switching the dial on the meter to the capacitor tester. Touch the probes to the ends of the capacitor as you did in the discharging of the unit in step 2. The meter should register either "good" or "bad" on the LCD display.

  4. Test the capacitor using the older analog type meter by first switching the meter to the "ohms" mode. You may have to move the red probe that fits in the meter from the "volts" connection into the "ohms" connector. The black probe wire should remain in the "common" connection.

  5. Place the red probe to one of the bare metal electrical connectors on the capacitor and the black probe to the other bare metal connector. Hold the probes in place for two seconds. You are charging the capacitor with the on-board battery from the analog mater. After two seconds remove the probes and reverse the connection of the probes to the capacitor. In other words replace the black probe with the red one and visa-versa.

  6. Read the meter as soon as you touch the probes to the capacitor. The analog type needle should "jump" to the right for just a slight moment. This indicates that the capacitor is storing a charge. You can conduct this test many times by holding the probes in place for two seconds and immediately reversing them. Every time you reverse the polarity of the meters probes, the analog meter should jump to the right. If the meter does not react, the capacitor could be defective.


  • Any capacitor leaking oil should be immediately and properly disposed of by following all local authority for disposal of hazardous waste. Some oils from older capacitors may contain harmful chemicals.
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