Quote:
Originally Posted by Old66Tiger
I am in the process of gathering all of the parts to set up my fans to run PWM with the use of a AC pressure switch. It will go in line with the trinary and should allow the fans to work on pressure rather than the state of the compressor clutch. I will be posting all of these parts once I get everything figured out.
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Unless you are using just an open/closed AC pressure switch in series with trinary, only way to use true AC pressure sensor is to wire to ECM and use it to control fan output based on AC pressure.
GM ECM's actually have an AC clutch output - issue is AC request comes from BCM (body control module) over CAN to ECM then ECM controls compressor. This allows feed-forward control of increased load from AC compressor to be accounted for - preventing RPM sags and droops. Given that most on this site are running V8's with considerable torque reserve (even at idle) usually not an issue without this functionality.
Lacking this capability (integrated BCM), best method is to use Vintage Air (or like) trinary switch to control compressor and AC pressure sensor wired (and calibrated) in ECM to control fans. Not quite OEM, but damn close (and way better than AC on=fan(s) on).
Dave