Yes, without climate control.
In answer to your first paragraph, The result was.... With the relay removed, across the terminals that power the relay, there is 12 volts regardless of the position of the A/C switch. When the relay was connected, the voltage dropped to zero, also regardless of the switch position. This indicates to me that there is little or no current to fire the relay. Am I correct in saying this?
Across those two terminals it should be 0V. With the relay in place, with respect to earth, there should be battery Voltage on both terminals unless the PCM is trying to switch the relay (and the A/C compressor) on in which case there should be 0V on the earthed side of the relay wrt earth. If the PCM is earthing the switching side of the relay then all the other components - A/C request input (the switch), BCM, pressure switch, refrigerant etc. and the connections between them - "upstream" have to be OK also.
Voltage and current is good from the positve side of the relay socket, as the compressor clutch engages when the relay socket is bridged.
I checked the wire between the relay and the PCM for continuity and all is good there. (It's actually XB. Light Green with a Black trace on my car).
If you earth that wire - at the relay is OK if you know the connection to the PCM is good - with the relay in place, in parallel with the PCM earth, then the compressor clutch should likewise engage.
The A/C light does not come on at all.
As that's switched by the BCM also,
if the A/C is 'on', that indicates to me that the BCM isn't going to be telling the PCM to switch the A/C on.
Holden said they checked the wire fom the A/C switch to the BCM terminal C9 and all was ok there.
D9 at the BCM? Red, white trace. It may depend on the BCM though.
I will check the voltage at the BCM, terminal B3 and let you know.
By way of explanation: B3 at the BCM is from the fan speed control so the BCM "knows" the HVAC fan is on.
As far as the voltage out of the pressure transducer, I don't know. That was checked by Holden. I will double check.
Wires:
Earth: F16 at PCM, black.
Pressure signal: B3 at PCM, green, black trace.
5V reference: B7 at PCM, violet, white trace.
I also want to check the data link wire between the BCM and the PCM.
I think I found the colour of the wire but would like to confirm it.....Tan with a Black trace. Am I correct?
Geoff.
I have the serial data connection between the BCM and PCM as red with black trace between D2 at the BCM and A3 at the PCM.
Other thoughts:
It's possible the idle flaring is the PCM correcting for an A/C compressor load on the engine that isn't there i.e. the PCM is earthing the A/C relay but there's a fault on that circuit somewhere. i.e. it's a symptom not a cause. That doesn't explain the A/C light not being lit though.
There is a wide open throttle cut out of the A/C via the PCM. Something there?
The BCM has to earth the blower inhibit relay via BCM B1, green wire, for there to be an input to the A/C blower input at BCM B3.
There has to be a thermostat input at BCM D4, green wire, for the A/C to be on.
BCM D9, red, white trace, is the A/C switch input (as ^).
BCM B8, red, brown trace, is the A/C LED earth.
The PCM switches off the A/C with refrigerant pressure too low or too high or coolant temp. too high.
