The contactor is the high-voltage switch inside your outdoor AC unit. When the thermostat calls for cooling, it sends a low-voltage signal that energizes a coil in the contactor, which snaps a set of contacts closed and sends 240-volt power to the compressor and condenser fan. When the thermostat is satisfied, the contactor opens and the unit shuts off. It is a small black box, usually with a visible plunger on top, and it switches on and off thousands of times a season. Over time the contacts pit, corrode, burn, or stick, and ants and debris love to get inside. A failed contactor is one of the most common AC no-cool calls: the unit either will not start at all, or it buzzes and will not shut off. It is inexpensive to replace but carries lethal voltage, so leave it to a pro. Call LA Heating & Air at (818) 660-1062.
