How to Replace an AC Capacitor

Capacitors are the heartbeat of your air conditioning unit, providing the initial jolt of energy required to kick-start the compressor and fan motors. When an AC unit hums but the fan fails to spin, or the house refuses to cool despite the thermostat running, the capacitor is the primary suspect. It is a simple, inexpensive electrical component that wears out over time, especially in high-heat climates where the system works overtime to keep your home comfortable. Performing this repair yourself saves hundreds of dollars in service call fees, provided you approach it with extreme caution and attention to detail. Success in this project is defined by safety—specifically, ensuring all electrical energy is fully dissipated before touching the terminals. When done correctly, your system will return to full functionality within minutes, and you will have gained a foundational understanding of your home's most critical cooling component.

  1. Kill the Power First. Locate the electrical disconnect box near the outdoor AC unit and pull the handle or flip the switch to the off position. For extra safety, turn off the dedicated air conditioner breaker at your home's main electrical panel as well.
  2. Document the Wiring Now. Remove the service access panel on the side of the AC unit by unscrewing the mounting fasteners. Once the panel is removed, locate the cylindrical capacitor, which is typically mounted to the side of the motor housing.
  3. Release Stored Electricity. Use an insulated screwdriver to bridge the gap between the terminals. Touch the metal shaft of the screwdriver across the common (C) terminal and the other terminals to short out any stored electrical charge.
  4. Disconnect and Remove. Disconnect the wires attached to the terminals, noting which wire came from which terminal. Unscrew the mounting strap holding the capacitor to the frame and pull the old unit out.
  5. Mount the New Capacitor. Slide the new capacitor into the mounting strap and secure it tightly. Ensure the microfarad (µF) and voltage ratings match your old unit exactly, as an incorrect match can damage the fan motor.
  6. Reconnect and Power Up. Attach the wires to their corresponding terminals on the new capacitor based on your reference photo. Reattach the service panel, flip the disconnect switch to 'On', and turn the breaker back on to test the system.