ac clutch

[tommy d]

I need help with ac on a 3.8 impala. The comp., accum., orifice was replaced with new parts, the system was flushed and vacuumed, and charged! Perfect! It cooled for one week, and now comp. clutch wont engage? Refigerent is still full; the high pressure switch is good; the cond fan runs as soon as you cut the ac on but no ac clutch engagement

[Blue Bowtie]

The possibilities are:

1. The PCM is not operating the clutch relay for some reason;
2. The clutch relay has failed;
3. The new clutch has failed;
4. There is a wiring/connector problem.

It might be easiest to locate the AC clutch relay and jumper it to see of the clutch and compressor are still operating. If jumpering the relay operates the clutch, exchange the relay with another of the same type (such as the horn relay) and see if the system operates. If the relay does not solve the problem, look upstream of the relay at the PCM and HVAC controls.

If the relay is not being operated by the PCM the refrigerant pressure sensor (analog) may not be reporting correctly to the PCM. Also, the PCM may be holding off the AC for some other reason such as lost inputs from the controls (the control head must be reporting to the PCM to enable the AC clutch), incorrect outdoor air temperature input, engine load calculation, and a host of other possibilities. If you have a bi-directional scanner available you could command the AC relay on and see if it responds.