If your central air unit fails to run, runs then stops, or you hear a humming sound, the capacitor may need replacing. A defective capacitor prevents the motor form getting the charge it needs to start. A capacitor cannot be repaired. You should be able to replace the capacitor yourself without advanced HVAC skills. Follow these directions to replace a central air conditioner capacitor.
Prepare to work
For this project, you need:
- work gloves
- voltage tester
- pencil camera or colored labels
- Phillips screwdriver or socket wrench set
- new capacitor
Turn off the power to the central air unit from the breaker box. An HVAC central air breaker commonly has two breakers. One breaker controls the compressor and the other breaker controls the blower. Turn off both breakers.
Turn the switch to the condenser unit on the outside to off. The switch is commonly located on an adjacent wall. Run the voltage meter rover the breaker box and condenser to ensure the central air conditioner is off.
Remove the Old Capacitor
Locate the access panel on the condenser. The access panel commonly has a warning label on it. Use the screwdriver to loosen the panel screws, detach the panel, and set the screws and panel aside.
The capacitor is shaped like a can or cylinder, and it may have a label on it. Write down all the data such as tolerance and load voltage on a piece of paper.
Note how the wires connect. You should see a "FAN" marking, a "COM" marking for common, and a "HERM" marking for the compressor. If there's no connection diagram on the unit, take a picture, or place colored labeling tape around the wires.
Remove the capacitor screw on the mounting strap with the screwdriver. Move the capacitor down, and turn it upside down.
To avoid shock, touch the blade of the screwdriver to the two terminals at the top of the capacitor. The pressure from the screwdriver will loosen stored charge. Disconnect the wires, and pull the capacitor out of the condenser.
Install the New Capacitor
Before you install the capacitor, check the microfarad rating. Connect a probe on the voltage meter to the "FAN" terminal., and repeat on the "COM" and "HERM" terminals. Compare them to the suggested ratings on the label.
Attach the new capacitor to the strap, and set it in place. Reattach the wires; referring to your photo or labels. Reinstall the access panel.
Restore power, and test the unit. If you don't trust your skill, or the unit still fails to work properly, contact an HVAC service.