I have an in-wall A/C unit that has been getting a workout in this 90 degree weather. It's a Kenmore Model No. 580.74124400. 115v 11.5A on a 15A dedicated circuit. I've now had two instances of the breaker tripping after the unit has been off.
The first time was after I had manually shut it off and it had continued to make noise. The interior fan was definitely off, and I believe the condenser fan was off as well (didn't go outside to check), but the compressor was definitely on. I could hear the tell-tale hum of the compressor, plus the hissing of refrigerant inside the unit.
I let this go on for about a minute before unplugging the unit from the wall and stepping outside to see if anything was visibly wrong with the unit. There's not a lot of visibility in the unit but I didn't see any damaged wires or tubing. I went back in and plugged the unit back in and it sat for several minutes before the compressor started up again all on its own. This time a couple minutes passed as I was trying to sort out what was going on and the breaker tripped.
I know that a breaker not instantly tripping is usually a sign of an overheat and not a short, so I was cautious to not leave the unit plugged in or running while we slept. Normally I set the built-in timer so it shuts off overnight. After several days of on/off without any issues I started to let it run on the timer overnight again.
Well after a couple nights of running it the breaker has tripped again. Nobody was awake to hear what the unit was doing, but based on the timing I have strong reason to believe it tripped after the unit had shut off from the timer.
I suppose the question is two-part. What is causing the compressor to run on its own when the unit is off? (It's not a physical power switch so I imagine the supply side of the relay is energized whenever the unit is plugged in) And what is it about the compressor running on its own that causes the trip? Is a compressor running without the fans causing an increased pressure or work load than if the whole unit was on?