How to Check and Replace an AC Capacitor Safely

Turn off power at the breaker, discharge the capacitor with an insulated screwdriver, then test with a multimeter or replace if bulging or leaking.

  1. Kill Power First. Switch off the AC unit at the thermostat, then turn off the breaker at your electrical panel. Wait 30 minutes for the system to fully power down. Remove the access panel on your outdoor unit using a screwdriver. The capacitor will be a small cylindrical or oval metal component with wires attached.
  2. Bleed the Charge. Even with power off, capacitors store electrical charge. Put on rubber gloves and use an insulated screwdriver to touch both terminals simultaneously for 3-5 seconds. You might see a small spark - this is normal. This step prevents potentially dangerous electrical shock.
  3. Read the Damage. Look for obvious signs of failure: bulging top or sides, brown or black burn marks, oily residue or white crusty buildup around the terminals, or rust. Any of these signs mean immediate replacement is needed. Take a photo of the wiring connections before removing anything.
  4. Verify with Precision. Set your multimeter to capacitance mode. Touch the probes to the terminals - the reading should match the microfarad rating printed on the capacitor label within 5-10%. If the reading is significantly low or shows no reading at all, the capacitor has failed and needs replacement.
  5. Extract Cleanly. Carefully pull the wire connectors off the terminals - they should come off easily. If stuck, gently wiggle while pulling. Remove the metal strap holding the capacitor in place, then lift out the old capacitor. Keep your photo handy for rewiring reference.
  6. Wire by Reference. Place the new capacitor in the mounting bracket and secure with the metal strap. Connect the wires to the correct terminals using your reference photo. The connections should be snug but not overtightened. Common terminal labels are C for common, HERM for hermetic compressor, and FAN for the fan motor.
  7. Confirm It Works. Replace the access panel and turn the breaker back on. Set your thermostat to call for cooling. The outdoor unit should start up within a few minutes. Listen for smooth operation without unusual clicking, buzzing, or grinding sounds. If the unit doesn't start or makes strange noises, turn off power and double-check your connections.