I have a 1997 Silverado ext. cab V6 with power door locks and windows & a/c, 145k miles. I've had to replace the a/c control unit in the dash 6 times in the last three years. I have not been able to get anyone to help me determine what makes them go out. The people at the dealershipsay just change the unit out. There must be something in the system that is causing the PC boards to fail. Is there a common root cause for this? How do I troubleshoot this?[/align]

 

Check the following circuits for a short to ground: [ol]Circuit 66 or Circuit 762 ( Gasoline Engines) Most common area is where the hvac compressor harness comes into the main harness by the left rear cylinder head.

Circuit 66, Circuit 603 and/or Circuit 762 ( Diesels Engines )

If a wiring checks out ok, replace the AC Low and/or High pressure switch for internally shorting out to ground. [/ol]

 

I'm not sure that I can find these circuits. What does Circuit 66, Circuit 603 and/or Circuit 762 go to. Maybe I can trace them from the source. Is there a way to troubleshoot the high and low pressure switch?