power surge on a/c compressor wire with all fuses off

You will need to trace the source of the power that is feeding the compressor through that wire. Typically, with all circuit breakers off, this would not be possible. I would start at the load center since that is the junction for all 120V and 12V wiring.

BTW, I assume when you say "surge", you are actually meaning that power is present, not an over-voltage situation. That is a different problem, entirely.