I spent some time this past week changing a compressor that had been deemed "failed" by one of our other service techs about a week ago. He had also ordered a condenser fan motor and stated on the work order that the comp was tripped out on high pressure due to the condenser fan failure. This made me wonder and decided to re-diagnose prior to going through the hassle of changing the comp.
I pressed in the contactor and the condenser fan turned on, but no compressor. Threw the amp clamp on, pulling 78 amps and then tripping on internal overload. I checked the capacitor and it was good, checked the windings of the compressor to each other and to ground and the readings were a little wonky, so I decided to change the compressor out.
I then went to do a start up and had the same problem, no compressor! It was pulling 78 amps and tripping out. I looked at the wiring diagram and noticed that the black and red wires on the load side of the contactor were reversed from the diagram. I flipped them not expecting any change because it is single phase 240 V at the unit, but low and behold it fired up and ran like it should. Black went to common on the comp and red went to Run (after changing the wires).
Why would it make any difference what wire went to the common or run terminal on the compressor? Isn't it the same voltage being applied to each leg?