Have a friend with a 2000 Monte and the compressor will not engage. I can jump the relay in the fuse box and it will engage. The a/c will cool. What signals the ground to bring on the relay for the clutch?

 

Its more than likely low on Freon...

It may get cool... But the system has to be full in order for the compressor to kick on..

 

and what if its full of Freon? mine has this same problem. everything new and full. i was told if it isnt ground issues it was pcm.

 

do a system reset....

unhook battery
take the + and - wires (which are no longer connected to the battery) and hold them together for 1 min.
reconnect and start car
check a/c

if it works, its your bcm needing to be replaced




if it still doesnt work, make sure it is not overfilled with r134a. a/c will not turn on if under or over pressurized.