How To Check And Test An HVAC Capacitor For A Non-Functioning Compressor

The compressor for your central air conditioning unit starts up the cooling process with a burst of compressed gas refrigerant. If the compressor doesn't start or operate properly, your HVAC system won't have the fuel it needs to provide cooling services. A suddenly non-functional compressor is often due to a problem with the capacitor.

A capacitor stores some electricity so that if the compressor experiences an interruption, the capacitor can step in with a boost to keep the system going. If the compressor breaks, the compressor will turn off at the next interruption and take your system along for the ride.

If you suspect your HVAC capacitor has broken, checking and testing the part for potential replacement isn't overly difficult if you own the right supplies.

Things You Need:

  • Owner's manual, as needed
  • Insulated screwdriver
  • Multi-meter with Ohms reading

Step 1: Find and Check the Capacitor

Turn off the electrical supply to the HVAC unit at the fuse box or circuit breaker. Use your owner's manual, if needed, to find the access panel that covers the capacitor. Remove the panel's fasteners and the panel to gain access to the capacitor, which looks like a tall cylinder with wires attached to terminals on the top.

Conduct a quick visual inspection for signs of dripping liquid or swelling on the capacitor. If you see either, leave your unit taken apart and call in an appliance repair service immediately.

If the capacitor looks healthy, continue on to the next step. 

Step 2: Drain and Test the Capacitor

Capacitors by definition hold an electrical charge so you want to drain the charge before testing. Lay the insulated screwdriver over both terminals on top of the capacitor and hold for several moments. Remove the screwdriver and carefully unhook the wires from the capacitor terminals.

Turn on the multi-meter making sure the readings are on Ohms. Hook one probe to the first terminal on the capacitor and then the other probe to the other terminal. Check the reading on the screen and make sure the numbers match up with the accessible range printed on the side of the capacitor. If the numbers don't match, you need a new capacitor.

If the capacitor does match the numbers, the problem might exist elsewhere in the system. The compressor itself can fail or experience severe continuity issues so you should really call in an appliance services company to ensure your air conditioning system comes back up and running to its full potential.