The contactor is an electrical switch in the condensing unit of your central air conditioner. The switch controls the electrical signal traveling between your indoor thermostat and that outdoor condensing unit. If the contactor is open, the unit knows to keep providing cooling services to your home while a closed contactor says to shut down shop.

A malfunctioning contactor can keep your air conditioner from turning on at all or keep the unit running well past the cooling level you desired. Replacing the contactor isn't difficult if you are confident this is the problem.

Things You Need:

•    Socket

•    Insulated screwdriver

•    Smartphone camera

•    New contactor

Step 1: Prep the Area

Turn off the power supply to the AC unit by removing the fuses from the disconnect typically located on the exterior wall near your condensing unit.

Use a socket to unthread the fasteners holding the access panel onto the main condensing unit body. Pull firmly down on the panel to remove it. Place the panel and screws off to the side somewhere you won't lose the fasteners.

Locate the run capacitor near the contactor. Hold the end of your insulated screwdriver over the terminals of the capacitor and wait a few minutes for the electrical charge to drain.

Step 2: Remove the Old Contactor

Use your phone to take a picture of the wires attached to the contactor so that you can have an orientation reference when it comes time to hook the wires back up. Note that little screws connect the wires to the contactor.

Loosen but not remove the screws holding the wires in place; you only need to loosen the screws enough to pull the wires free. Use your socket to unthread the mounting screws holding the contactor to the condensing unit wall. Save the mounting screws then discard the contactor. 

Step 3: Install the New Contactor

Position the new contactor in place using the mounting screw holes as guides. Use your socket to thread the mounting screws through the contactor and into the condensing unit wall. Make sure the fasteners are tight, or the part could fall off.

Consult your picture of the wire orientation and use the guide to reattach the wires under the screws on the new capacitor.  Loosen the screws a bit first to have an easier time getting the wires attached. Tighten the screws up once all of the wires are in position.

Replace the access panel over the area and attach its fasteners. Restore power to your unit and check for operation. If the unit still has problems, contact an air conditioning installation and services company, such as Action Air of Florida, for help.