Hoping someone can help me narrow down a diagnosis. I have a window AC unit that is having issues starting the compressor. I’ve tested the thermistor, compressor, control board and capacitor and all seem to be working. What I know for sure is the compressor will not even try to start while the fan is running. Here is what I have done:

Using glasses of hot and cold water, verified the thermistor is measuring temp through the digital display and actuating the compressor switch. I removed one of my fan speed cables so I have a dead fan circuit on one speed, When I am on the dead speed, the compressor switch engages with a nice sold click. The loud hum of the compressor starts and the unit beeps like it does when a cooling cycle starts, then the whole unit immediately shuts off. I’m guessing that’s a safety interlock since the fan isn’t spinning.

Doing the same thing on an active fan speed circuit, the click to engage the compressor is barely audible and it never starts. I suspect the capacitor, but I’ve tested it with a meter and both the fan and herm capacitors are reading the rated capacitance. No terminals are showing shorted to ground and the top isn’t deformed at all. The center of the bottom does protrude a bit so it doesn’t sit flat. No oil visible around the rim, though there is some gold-colored substance at the center of the terminal plates.

Checking the terminals on the compressor yielded low ohms readings and no shorts to ground. Anyone got any ideas? What did I miss?

Edited by user Wednesday, August 11, 2021 5:11:45 PM(UTC)  | Reason: Not specified