A York condenser that wouldn't shut off: the contactor's contacts had welded
A recent job in the Los Angeles area, September 2026. A tap on the contactor released it, and the photo shows the burn marks around its contacts.
In this guide
The complaint: an outdoor unit that wouldn’t turn off
A customer’s York air-conditioning condenser wouldn’t turn off. The outdoor unit just kept running.
A tap, and it let go
When I got there, I tapped the contactor, and it released. That meant its contacts had stuck together, welded, so the switch stayed closed and the outdoor unit kept getting power.
A tap can free welded contacts, but it doesn’t make them good again. They’re already burnt, so the contactor gets replaced.
What the photo shows
In the photo at the top of this page, the contactor is in my glove, next to the condenser’s open electrical compartment, where the capacitor and the bundle of colored wires sit.
Below is a close-up of the same photo. Look at the window in the middle of the contactor, where the contacts meet: you can see the burn marks around them.
The fix
We replaced the contactor, and everything worked normally. The outdoor unit now shuts off when it should.
What a contactor does
The contactor is the switch for the outdoor unit. When the thermostat calls for cooling, it sends a low-voltage signal to the contactor’s coil. The coil pulls the contacts closed, and line voltage flows to the compressor and the condenser fan. When the thermostat stops calling, the coil lets go and the contacts open.
Why contacts burn and stick
Each time the contacts close or open under load, a small arc jumps between them. Over many cycles that arc pits and burns their surfaces. Pitted contacts heat up, and hot, rough contacts can stick together. Then the switch stays closed after the coil lets go, and the outdoor unit keeps running, which is what happened here.
A contactor can also fail the other way and stop closing, so the outdoor unit won’t start. We wrote up a condenser with a stuck contactor that turned out to be the third fault on the same unit.
What you can do
If the outdoor unit keeps running when the thermostat is off, switch the system off at the thermostat. If it still runs, turn off the AC breaker in your electrical panel. Then call.
Don’t open the condenser’s electrical cover, and don’t tap the contactor yourself. There’s line voltage inside, and the capacitor can hold a charge even after the power is off.
AC repair in Los Angeles
We repair central AC condensers across the Westside, Hollywood and the San Fernando Valley. The $85 service call is credited toward the repair if you go ahead, and repairs carry a 30-day labor and 90-day parts warranty. CA BEAR registered (#A 50636), EPA Section 608 Universal certified. See our HVAC services or call (213) 205-2055.
FAQ
What does an AC contactor do?
It's the switch for the outdoor unit. When the thermostat calls for cooling, a low-voltage signal pulls the contactor closed, and line voltage reaches the compressor and the condenser fan. When the thermostat stops calling, it opens.
Why does my outdoor AC unit keep running when the thermostat is off?
A contactor whose contacts have welded together is one possible cause: the switch stays closed, so the compressor and the fan keep running. A thermostat or wiring fault can do the same, so it needs testing. On this York, a tap on the contactor released it, which showed the contacts had stuck together.
Why do contactor contacts burn and stick?
Each time the contacts close or open under load, a small arc jumps between them. Over many cycles that pits and burns their surfaces, and pitted contacts run hot and can stick together. On this York the photos show the burn marks around the contacts.
Can I tap the contactor or replace it myself?
We don't recommend either. The compartment carries line voltage, and the capacitor next to the contactor can hold a charge after the power is off. Contacts that let go after a tap are already damaged. Turn the system off at the thermostat, and at the breaker if it keeps running, then call.
Do you work on York AC units in Los Angeles?
Yes. We service central AC condensers from York and other makers across the Westside, Hollywood and the San Fernando Valley. The $85 service call is credited toward the repair if you go ahead.
AC, heater or mini-split acting up? We cover LA and the Valley.
Call (213) 205-2055 or text a photo of the unit and its model sticker.