LT1, OBD1, Tunercats, verified this a dozen times tonight, A/C will not kick and start pumping until engine RPM exceeds 2,000. Doesn't matter which gear (manual). Doesn't matter what MPH.

Completely lost on this one.

 

Does the PCM show an AC request the moment the switch is put in the AC position or is that delayed as well?

 

It shows the A/C Request immediately, and it does in fact close the relay. But the clutch solenoid on the physical Pump appears to wait until exactly 2,000 RPM to engage, and disengages at 1,999 RPM and below.

 

aiflaw, Assume you have a DataMaster trace.. The a/c request line is directly off the dash switch, next the a/c clutch relay line is activated by the PCM if all is OK, you should then see the a/c clutch status line activate. The clutch status is the +12 volt output of the a/c relay sampled between the relay and the clutch. If the a/c relay is picked and the clutch status is on then you either have a physical circuit break between the s105 splice (see url) and the clutch which is hard to believe since it's tied to RPM. Or it could be the clutch is slipping at engine speeds below 2K ?? Do you physically hear the clutch pick and drop out between say 1000 and 2000 RPM, or does the compressor just not spin and put out any pressure before 2K. Does the clutch status line change between 1K and 2K. I'm trying to isolate to either an electrical, or a physical clutch problem with these questions, so bear with me. Once you see clutch status activate on the trace you should see a/c pressure start building regardless of engine RPM. Schematic ref shbox.com http://shbox.com/1/hvac_compressor_control.jpg

 

sounds to me that the clutch plate needs to be adjusted inward on the compressor. The magnet of the compressor clutch isnt strong enough to pull the plates together at lower rpm. Go to AZ and rent there AC clutch tool box and readjust the air gap of the compressor clutch plates.....

 

I've got datamaster logs, it calls for the relay, the relay does click in, the clutch is either fully engaged, or not engaged, and at exactly 2000 it engages.... I like the last response, although I've never heard of it. sounds very interesting.

 

The "gap" theory is probably right however it is not clear whether it's adjustable on these clutches. So I advise you confirm there is good voltage and ground at the clutch coil while the engine is idling. If so, it's time for a new compressor/clutch combo.

The GM shop manual gives the gap as .020 - .030. The shop manual merely tells you to install the plate assembly with an installer. It does not tell you check and adjust as needed. Leading me to believe that it bottoms out and is to have a certain gap. If it is beyond the gap it's time to change it.

Therefore if it has voltage and ground to the coil and it doesn't pull in, it should be changed.