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What Does An AC Contactor Do?

What Does My Air Conditioner’s Contactor Do?

The capacitor and contactor work hand in hand to keep you air conditioner running all summer long.

ac contactor image

AC Power Center

Along with the capacitor, the air conditioner’s contactor works all summer long to keep power flowing to your air conditioner’s most important parts.

The contactor is essentially a type of switch that receives a low voltage signal (24V) from your furnace to power on.

By creating a magnetic field, it pulls down a piece of metal that will connect both of the higher voltage sides.

This closing of the circuit allows electricity to power the air conditioner’s fan and compressor motors.

Contactors come in generally two different types: single pole and double pole.

A single pole contains one magnetic coil that will connect one circuit.

A double pole is essentially the same thing but it has two coils and connects two circuits. 

How To Know If A Contactor Is Bad

One of the most classic signs a contactor has gone bad is a loud “chattering” type of noise coming from your outside condenser unit.

Without a chattering noise, the best way to diagnose a bad air conditioner capacitor is to use a multi-meter device that measures the flow of electricity.

Also, you may notice that some of the contacts on the contactor itself may have become pitted and worn down which happens naturally over time as the contactor ages.

The average lifespan of a good contactor can be anywhere from 5-10 years assuming the unit is taken care of with annual maintenance each year.