How To Test And Replace The Run Capacitor In A Hard Starting Central AC

Does your central air conditioner's compressor start, shudder, and then suddenly stop? This type of hard starting can be due to a failing or broken run capacitor. A run capacitor helps the compressor run with a constant but stable electrical current. A failed run capacitor can make the compressor unstable and cause hard starting. Testing and changing a capacitor is a task you can complete with a multi-meter and a few basic tools.

Note that this project does require some active electricity. If you aren't confident handling live electricity, call in an AC repair technician to perform the test and replacement.

What You Need:

  • Socket wrench
  • Insulated screwdriver
  • Pliers
  • Multi-meter
  • New run capacitor

Step 1: Test the Old Run Capacitor

Turn off power to the condensing unit by removing the fuses from the disconnect box or by flipping off the appropriate circuit breaker.

Use a socket wrench to remove the fasteners on the access panel. Remove the access panel cover and set the cover aside. Locate the run capacitor and make note of where the terminals are on the top. Don't remove the wires yet. Touch the end of the insulated screwdriver across both terminals of the run capacitor to discharge the stored electricity.

Examine the run capacitor wires and make note of how the wires are attached. Use pliers to disconnect the wires.

Set up your multi-meter by turning the settings to Ohms. Place one multi-meter probe to each of the run capacitor terminals. Check that the reading on the meter matches the range of Ohms listed on the side of the run capacitor. If the range doesn't match, you need to replace the part. If the range does match, you need to keep troubleshooting or call in an air conditioning repair company for assistance.

Step 2: Remove and Replace the Run Capacitor

Remove the mounting screws on the fastener bracket using your socket wrench. Slide the capacitor out of the bracket. Dispose of the old capacitor.

Insert the new capacitor into the bracket slot. Attach the mounting screws to secure the capacitor. Hook the wires up to the terminals in the correct orientation.

Place the access panel door back over the entry and connect the fasteners. Restore power at the fuse box or circuit breaker. Turn on the thermostat to trigger the air conditioner into running and check for the hard start. If the problem persists, call in an HVAC technician.