Ac Compressor won't shut off

[mark0224]

I have a 13500 btu AC the fan shuts off but the compressor continues to hum until you trip the breaker. Was working fine all week but was on a lot because it was very hot out last week. Looking for input on why and how to fix.

[boondocking]

Will it restart 5 min later when you click breaker back on or does it start to hum again? If it does nothing then lower the stat and tell us what happens.

[Bama Rambler]

Sounds like a bad thermostat.
There was a thread describing the same symptoms a while back and it turned out to be a bad t-stat.

[mark0224]

Boon it starts humming right away even a day later.

[mark0224]

Going to check tstat first then go on from there saw something about a relay welding itself shut causing this also will be cking that too

[Mr. Dan]

In a previous trailer, I had a compressor that wouldn't shut down unless I flipped off its breaker. I read about a test wherein the yellow wire should be pulled from the thermostat. The article said if the compressor kept running after the yellow wire was pulled from the thermostat, the control board in the A/C unit was bad. I took it to the service dept. of my selling dealership and the service manager said, "Yeah, right" as if a customer could not possibly know. They called Dometic who told them to run the test I suggested. It failed. Dometic sent a new control board and paid for its installation.

[Bluepill]

Try to find a manual for your thermostat with a Google search.

1. Disconnect the compressor control wire (often yellow) at the thermostat and see if the compressor shuts off. If it does.............

2. Test the voltage at the compressor control wire terminal and see if it is still activated when the thermostat no longer calls for cooling. If so, bad thermostat.

Edit: Dan beat me by a minute.

[boondocking]

If the compressor just hums and does not start which you would be able to hear, the start capacitor is more than likely no good.

Grab yourself one of these to replace the old capacitor and you should be good to go.

The hum you are hearing is the motors windings. The start capacitor gives a boost of amperage to the windings to get the armature turning. Without that amp boost the armature can not start to turn so the motor sits there and hums.

[bob dirt]

Saying that it starts right away even a day later leads me to believe it's the control board. If it was the thermostat, the compressor would not start right away after power is turned back on do to the built in time delay on the board.You could probably smack the relay on the board with thermostat turned off and the compressor may turn off and run normal, but it would probably stick again after running for a while.

[boondocking]

Originally Posted by bob dirt

Saying that it starts right away even a day later leads me to believe it's the control board.

OP says it hums, but does not start.

[bob dirt]

Originally Posted by boondocking

OP says it hums, but does not start.

Yep, that's what he says, but he also says it won 't shut off till he shuts off breaker....that leads me to believe it is actually running which will sound
like it's humming. If it was a bad capacitor, it would shut itself off due to overload on or in compressor....just say'n

[mark0224]

Maybe I have not stated right if I turn the fan to on or auto and turn the breaker on it starts blowing cold air. But if you turn it off compressor continues to hum fan stops.

[bob dirt]

Are you going to try and fix yourself or is it in warranty? What state are you from?

[mark0224]

Going to start with the basics t stat and a relay i found could be the problem when i googled the problem. If looking at those doesn't come up with a result I will probably have somebody look at it.

[mark0224]

Think I got it figured out, as others have said I believe its the control board. I put the old analog t stat in and it still did it , found the compressor relay on the board and unhooked it and it didn't happen anymore. that relay is supposed to be a normally open so I believe its the problem.

[mark0224]

Thanks all for the input replaced the compressor relay control board today and everything seems to be working right so far. Came with new digital thermostat and an updated digital board. Less wires, not a lot of instructions only downfall.

[Mr. Dan]

Thanks for reporting back with the solution to your problem. This reporting back helps our members!

[mark0224]

I know and glad to help others, and was really glad I could fix it myself.

[mark0224]

Old control that came out of my ac unit

[mark0224]

New control all wired in tested while still all open . Be careful while electric is live if you test like this.