Nissan Repair: 94 pathfinder A/C grounding issue, relay switch, pressure switch

Question
The air conditioner on my '94 pathfinder has not worked for some time.  Today an engineer friend troubleshot it down to lack of grounding in the relay switch that controls the compressor (compressor kicked on when he grounded the relay).  He showed me how to create a new ground, but we were wondering where the original ground for this relay switch originated from, in case we may accidentally bypass a failsafe.

Answer
Mike,

The relay gets its ground from a pressure switch that prevents the compressor from activating if the system is low on refrigerant.  Check the system pressures as soon as possible to make sure you have enough refrigerant otherwise the compressor could be damaged.