How to Install an Air Conditioning Start Capacitor

Air conditioning motors require a substantial amount of power when they start. A start capacitor supplies the motor with a burst of additional electrical power for the start-up cycle. When a start capacitor fails, the motor produces a telltale humming sound when electrical power is sent to the capacitor. The motor may eventually trip the air conditioner's built-in overload protection circuit, which in turn shuts down the air conditioning unit. You can install a new start capacitor with the proper tools and electrical circuit knowledge.

Phillips screwdriver
Flathead screwdriver
Voltage tester
Marker pen
Socket driver set

Instructions

- 1
  Turn off the electrical supply breaker to the air conditioning unit at the main panel. Also place the exterior switch to the "Off" position if one is present. Tag or mark the switch and breaker to alert others of the work being done.
- 2
  Remove the electrical access panel screws of the air conditioning unit using the appropriate screwdriver.
- 3
  Find the start capacitor. Most units feature both a start and a run capacitor. The start capacitor is cylindrical in shape and approximately five inches long and two inches in diameter.
- 4
  Place the metal shank of the screwdriver across both terminals on top of the capacitor to short it out and remove any charge left in the capacitor.
- 5
  Test the capacitor terminals with a voltage tester to ensure no latent power exists. Place one test probe on one terminal and the other on the other.
- 6
  Mark the two wires connected to the old start capacitor to identify them for installation on the new capacitor. Most units have color-coded wiring, but if yours does not, hash marks made with a marker pen will do the job.
- 7
  Remove the wires from the old capacitor using the appropriate-size socket driver. Turn the terminal nuts counterclockwise.
- 8
  Loosen the start capacitor retaining strap screw with a screwdriver. Pull the old capacitor up and out from the air conditioning unit.
- 9
  Put the new capacitor in the retaining strap. Tighten the strap screw.
- 10
  Connect the wires to the correct terminals according to the marks you made or the color code. Tighten the terminal clockwise with the socket driver.
- 11
  Press the reset button for the air conditioner's overload protection device. Check your owner's manual for the reset button location as it varies from manufacturer to manufacturer.
- 12
  Replace the panel cover and screws. Tighten the screws clockwise.
- 13
  Restore the power to the air conditioning unit and remove all tags and markings.

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