How to Replace an AC Capacitor or Contactor (Step-by-Step Guide)

If your AC won’t start or the outdoor unit hums or clicks, a failed capacitor or contactor is often the cause—and these parts can sometimes be replaced safely with the right precautions.

If your central air conditioner is not working at all, one of the most common causes is a failed capacitor or contactor in the outdoor unit. These small electrical components control and start the compressor and fan—and when they fail, the system won’t run.

See: AC Not Turning On | AC Compressor Not Working

Quick Answer

If your AC clicks, hums, or won’t start, check the capacitor and contactor. These are common failure points and are relatively inexpensive to replace.

Bottom Line: This is a common DIY repair—but only if you are comfortable working safely with high-voltage components.

Signs of a Bad Capacitor or Contactor

• Clicking sound: Contactor engaging but system not starting
• Humming or buzzing: Capacitor failing to start motor
• Fan not spinning: Capacitor problem
• Outdoor unit not running: Power or contactor issue
• Intermittent operation: Worn electrical contacts

See also:

• AC Capacitor Symptoms
• AC Contactor Symptoms

⚠️ Safety First

If you are not experienced with electrical work, skip this repair and call a professional.

How to Replace an AC Capacitor

Step 1: Turn Off Power

Shut off the thermostat, turn off the breaker, and pull the outdoor disconnect to completely cut power to the unit.

Step 2: Access the Electrical Panel

Remove the screws holding the service panel in place and carefully open it to expose the capacitor and wiring.

Step 3: Discharge the Capacitor

Use an insulated screwdriver to bridge the terminals and safely discharge any stored electrical charge.

Step 4: Document Wiring

Take a clear photo of all wire connections so you can reconnect them correctly later.

Step 5: Test the Capacitor

Use a multimeter set to capacitance to confirm whether the capacitor is within its rated range.

Step 6: Replace the Capacitor

Install a new capacitor with the exact same voltage and microfarad rating, then reconnect the wires as shown in your photo.

How to Replace an AC Contactor

Step 1: Turn Off Power

Shut off all power to the system at the breaker and disconnect before working inside the unit.

Step 2: Open Access Panel

Remove the service panel to access the contactor and surrounding components.

Step 3: Inspect the Contactor

Check for burned, pitted, or stuck contacts and look for debris or insect buildup.

Step 4: Document Wiring

Take a photo of the wiring connections to ensure accurate reinstallation.

Step 5: Replace the Contactor

Install a matching contactor and reconnect each wire to the same terminal as before.

AC Capacitor and Contactor Repair Cost

• Capacitor: $150–$400 installed
• Contactor: $150–$350 installed
• DIY parts: $20–$60

See: Central AC Repair Cost

When to Call a Pro

• You are unsure about electrical safety
• Breaker trips repeatedly
• Compressor won’t start after replacement
• Wiring appears damaged

NEXT SEE

• AC Not Turning On
• AC Compressor Not Working
• AC Capacitor Symptoms
• AC Contactor Symptoms
• Central AC Repair Cost