How and When to Change A Contactor

You might consider changing a contactor when there is a significant voltage drop, which can drop the voltage to the compressor and reduces the system capacity. An overheating contactor is also exceptionally prone to failure, and it might be time for a replacement (especially in three-phase systems).

Bert and Kirby come across a pitted contactor when performing a visual inspection on a maintenance procedure. Bert shows the difference between a pitted contactor and a new one, and he explains how voltage passes through the contactor and why the system might suffer from a performance drop.

Once they receive the go-ahead to replace the contactor, they shut off the breaker outdoors AND indoors, as there is low voltage on the other side of the coil. (On a heat pump system, you could also disconnect the wires from the defrost board to get rid of that low voltage at the contactor. In any case, be sure to use a meter and compare the voltage to a known power source.) Kirby removes the contactor, and Bert uses that old contactor to show how arcing is responsible for the contactor’s condition.

The connection needs to be clean when the compressor starts up because the contacts pull in when the compressor has the highest amp draw. Locked rotor amps draw higher current than the usual run current, and all of that current has to pass through the contactor. If the connection isn’t clean or has too much of a voltage drop, you risk compressor failure.

Bert cuts off the end of the spade connector, which could create a stronger connection when used with anti-corrosive electric grease. (However, you risk making your connection poorer by using it.) Kirby secures the contactor before he attaches the wiring to it.

During the inspection phase, Bert teaches Kirby how to read the schematic. Kirby uses the schematic to confirm the proper wiring of the system before turning the system on. It’s also a good idea to have an amp clamp on the compressor lead so that you can monitor the amperage as the system powers on.