THE SHORT ANSWER
The contactor is the switch that turns your outdoor unit on. To replace it, match three numbers.
- Poles: 1 or 2. Count them on the old one.
- Coil volts: must match. Most homes use 24 V.
- Amps: same or higher than your old one.
Safety first
A contactor carries 240 V. That can kill. Turn off the breaker and pull the outdoor disconnect. Then test the wires with a voltage tester before you touch anything. The capacitor next to it can hold a charge too.
Not sure how to test for power? Call a licensed HVAC tech. This is a short job for a pro.
1What a contactor does
When your thermostat calls for cooling, it sends a small 24 V signal to the contactor coil. The coil pulls the contacts closed. Then full power flows to the compressor and the outdoor fan.
2Signs it is worn
- The thermostat calls for cooling, but the outdoor unit stays off.
- The outdoor unit keeps running when the thermostat is off. The contacts may be stuck closed.
- A loud buzz or chatter from the outdoor unit.
- Burnt, pitted or black contacts.
Ants and bugs can also get stuck in the contacts and stop them from closing.
3Match the numbers
- Poles: a 1 pole contactor has one switched pair plus a metal bar. A 2 pole has two switched pairs. Match your old one.
- Coil volts: printed on the coil. Most homes use 24 V. It must be the same.
- Amps: the FLA or inductive amp rating, like 30 A. Use the same or higher.
4How to swap it
- Turn off the breaker and pull the disconnect. Test for power.
- Take a clear photo of every wire.
- Move the wires one at a time from the old contactor to the same spots on the new one.
- Mount the new contactor with the same screws.
- Close the panel. Restore power. Set the thermostat to cool and check that the outdoor unit starts.
When to call a pro
Call a licensed tech if you cannot test for power, if any wire looks burnt or melted, or if a new contactor burns out quickly. A contactor that keeps failing can point to a bigger problem.
Ready to match the numbers?
Filter by the specs printed on your old part.