I had the exact same problem. It was the AC compressor clutch coil. The pulley bearing on the compressor had gone bad and ground into the windings of the clutch coil. To isolate this you can either unplug the wires from the compressor or remove the AC relay from the underhood fuse box. Have you noticed any noise under the hood? My AC finally locked up. the compressor still turned OK but the pulley bearing was shot. The car would not even turn over as it held the belt still. It ended up putting in a used compressor and it's been fine since.
