My dad has a 93 chevy cheyenne with a 4.3 v6. A couple weeks ago I added some freon to the system and everything was fine. After running the system for two or three days it stopped working. After looking over it I see the compressor is not kicking on. When I jump it, it comes right on. I can't find any relays or disconnected wires. What else should I be looking for to fix this?