Easy A/C or heat pump fix

bczoom

Super Moderator
Staff member
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My heat pump quit working properly. In my case, it wouldn't turn off even though there was no demand for heat. Had to use the circuit breaker to shut it down. Called my HVAC guy and he was pretty tied up but would come out if really needed. I was in no hurry since I can heat using the wood stoves so he said it would be about 5 days before he would be there.

Well, the tinkerer that I am, I decided to play with it. An internet search of the issue coupled with a couple youtube videos pointed me towards the potential issue.

Inside you heat pump or A/C unit, there's what's called a contactor relay. It takes a 24 volt signal from the thermostat which tells the unit to either turn on or off. That 24 volts incokes a magnetic coil to open or close which activates your 110/220v power to the unit to make it run. Well, my coil activation was stuck in the closed position so the heat pump wouldn't shut off.

With the power OFF, I pulled the cover off the heat pump, located the contactor and using needle nose pliers, pulled on the little tab attached to the magnetic coil and got it freed up. Sure enough, once I turned on the breaker, the heat pump was working again but I knew I was on borrowed time. I ordered a new contactor for about $15. Installation took about 30 minutes.

So, if your heat pump or A/C unit starts acting up, this is something worth looking at. This contactor going bad can also give your unit a buzzing noise or low voltage situation.

Here's what it looks like. Some are larger and have a couple more poles.
 

waybomb

Well-known member
GOLD Site Supporter
I had the opposite problem on a new home purchase. The heat pump/ac would not turn on. Our stuff hadn't arrived yet, so I went and met my new neighbor, borrowed a couple tools, took it apart, put some cardboard in between the backside of the contacts and the body of the contactor, and I had AC. Got pretty cold at that night in the house, but much better than what seemed like 90f/90% humidity. Picked up a new contactor next day.
 
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