I have a 94 Sierra 4X4. The fan controller seems to have lost power. I have checked the blower motor, I have changed all the relays, and the rectifier. I picked up a couple of fan controllers from the wrecking yard. When I put one the new controllers in the system "woke up" for a few minutes but then went dark again. I have checked the controller in another truck and it works fine. Any ideas what else i should check. It is an electrical issue but i can't pin it down. I haven't been able to find a decent schematic and I don't know if there is another relay that I have missed or possibly a circuit breaker or fuseable link. Any suggestions would be greatly appreciated.
