My trane heat pump trips the outdoor unit breaker at startup. It stays set when compressor is not running. I changed the contactor because it was arcing, but still have a problem. What's the best way to test compressor and fan motor for short.
With a digital meter. Take the cover off of the heat pump so you have access to the comrpessor wiring terminals. Remove the wires (write down which wire goes to each terminal first!) and with the use of a digital meter test for continuity (ohms) from each terminal to ground. You can use the copper refrigerant line going into the compressor as ground or the cabinet of the heat pump but you'll need to have to scratch the paint off to be able to touch metal.
If from any of the terminals to ground show continuity then the compressor is "grounded" and is why the breaker is tripping. This means the comrpessor is no good and you need a new one.