How to Test an AC Unit Capacitor

Air conditioning systems use capacitors when the motor begins and when the motor runs.

Testing your AC capacitor can help you save money.Testing your AC capacitor can help you save money.
Each capacitor unit contains a start capacitor and a run capacitor. Malfunctions with either of these devices can cause the air conditioner to run improperly or not run at all, which can lead to long-term damage to the compressor. Testing a capacitor saves money by alerting you to replace it as soon as it becomes defective. This is inexpensive compared to having to replace the capacitor as well as other, more costly components that malfunctioned directly as a result of its failure.

Turn off the circuit breakers that run the air conditioner, including the outside contactor located near the outdoor unit of a central air conditioner.

Disconnect the wires that supply power to the motor using the wire cutters and the appropriate screwdriver. Some connections use Phillips screws while others use straight-edged screws. Leave the wires that run from the capacitor to the motor connected for the time being.

Ohm meters measure the amount of electrical current.

Turn the volt-ohm meter to the volts position. Create the testing circuit by connecting the leads from the meter to the wires of the capacitor. Hold the leads in place until the meter reads zero.

Disconnect the wires that connect the capacitor to the motor. Switch the meter to the ohms setting. Hold the leads on these wires for a count of three while the electrical current from the meter charges the capacitor.

Reverse the position of the leads on the wires of the capacitor by switching the places of the black and red wires coming from the volt-ohm meter.

Replace the capacitor if the meter doesn't move toward infinite ohms. Failure to move toward infinite ohms indicates a bad capacitor.

Things You Will Need

  • Safety glasses
  • Volt-ohm meter
  • Screwdriver
  • Wire stripper

About the Author

Charlie Bradley has been a freelance writer since 2007. Bradley's work has been featured on various websites. He holds a certificate in personal computer repair and support from West Georgia Technical College.