There is a relay behind the glovebox. You should hear a faint click when you switch the ac on. If this is working, its not the high pressure switch you should jump but the low pressure switch which is located on one of the refrigerant lines leading through the bulkhead on the engine side. Short this to make the compressor come on. Just try it for a second or two coz the oil wont be circulating properly if you are low on gas and your compressor may get damaged.