2000 GMC air conditioning problem

Factual Questions
1

I having air conditioning problems with my 2000 GMC Sierra. The air conditioing works when it is first used, but it stops blowing cool after a few minutes or after either the car is restarted or the AC is turned off and then back on. I’ve checked and the compressor is disengaged.

Freon pressures (static, low and high) read as ok for the outdoor temp (no apparent over or undecharge and no orifice obstruction or weak compressor), and the low and high pressure switches have voltage. Bypassing the switches does not help.

Now, here’s the kicker–I checked voltages at the AC relay in the fuse panel at a time when the compressor would not turn on. Both the signal line and the power for the clutch had voltage. Jumpering the clutch voltage gives voltage at the connector to the clutch, but the clutch will not turn on. I haven’t ohmed out the clucth coils, but is it possible for the clutch to fail to activate when hot? Alternately, is there anything on the ground side of the compressor clutch, or is it a direct line to ground?

2

Sure, the clutch could have a break in it’s coil, which would only fail when it heats up.
If you have 12v at the clutch, and it’s not engaging, its bad.

3

Check and see if your clutch has a ground wire before you assume it is bad. Sometimes ground wires also go through switches or safety devices. Not sure on your vehicle.

Just for reference, a static pressure reading on your a/c system will not tell you anything about the amount of freon in the system. Once the freon is at the saturation point it will read the same from one drop of liquid freon to a full charge.

4

Thanks, folks. I metered the ground line from the clutch, and it does go to ground with no resistance. I’m calling a shop.