The compressor circuit has a low pressure switch, over just behind the core support on the pside. If you don't have enough pressure on there, the compressor won't run. Can't remember if the condenser fan is on the same circuit. I won't refer you to the wiring diagram. The a/c system wiring is incredibly complex, and you'll be chasing wires around in circles. It has about 3 diodes in the circuit, and if you don't catch them, the wiring makes no sense at all. There is also a thermo switch that kills the a/c if it doesn't ground like it's supposed to. On the water neck, small single wire. If you have an a/t, it also kills o/d.