Thanks Maverick. Turned out to be one of the wires going to the reversing valve at the compressor. It had laid up against the copper tubing and melted so that when the unit went into "defrost mode" (it's been relatively cold in Charleston so it reversed frequently) it would short out and pop the fuse. Explains why it would run for an hour or so before failing. Anyway, seems to be working now.
I just wish the weather would warm up!