Through disconnect switch shutting off power to the condenser unit. Test the compressor for open circuit and short wih ohm meter (ohms resistance not amps). Disconnects power leads on the compressor. Test acrossed the leads should get some reading verifying continuity (no reading results of an open circuit) and then test each lead to the compressor housing, should not get a reading, if so compressor is shorted to ground. It has been 40 years and that is about all I remember.