■ Use ohmmeter first to check unit continuity ground.
In checking for a ground in either section, power supply disconnects should be open. This prevents any accident from occurring due to a feed back of power. There are times when only one fuse opens letting electricity flow through the good fuse. With disconnect open, check from the load side of the circuit being tested. In the case of the condensing unit, check the compressor contactor. If a ground is indicated, all of the circuits must be isolated including the compressor, condenser fan motor, crankcase heater, and any other electrical device that may be wired to the unit. This also applies to the evaporator section when it is tested.
At times, a ground can develop in the supply circuit itself that would cause the circuit to open. In cases like these, your responsibility is over. The electrician should be notified that you are to be informed when the power supply circuit is repaired.
The third reason for power supply to open is an overloaded circuit. The demand exceeds the rating of the protection device.