Could very well be a relay, but it's been my experience on those cars that the cycling switches tend to go bad, usually a relay will just burn out creating an open cicuit and not a short to ground.
True, relays are normanly open. And if they fail they just stay open.
you may have too much on that line, try some other outlet that isn't on the same breaker. In fact, run an extension cord from some outlet not on the same breaker as the ac now, and if it isn't shutting down then you are currently overlaoding the outlet where the ac now is plugged into, and either change the amps or feed different appliances to different zones
Have the compresser checked out