I'm getting closer! For everyone's info - it's the ECU that controls the air con pump - it's a complicated set up to say the very least! I think my ecu has an issue.

For reference, when my ignition is on and the engine is NOT running should the idle control valve buzz continuously?

 

Well I've 'fixed' it by removing the connection to the ECU that goes negative after 10 seconds or so and connecting it to the CCU wire (that also goes to the ECU - this is connections N143 M143). Everything now works as it should with the exception that when I view the ecu heater inputs using scantool it says that AC switch is closed and compressor is activated regardless of any CCU settings. I also get error 170 which is A/C control

I'm thinking that there is either another control wire that goes between the CCU and the ECU that's faulty OR there's an ECU fault.

To simplify, a wire runs from the CCU to the pressure switch and to the ECU plug 20 pin 14 and then should continue on to the relay. From the relay it should then go back again to the ECU via PIN 12 (plug 20). This doesn't seem to actually happen. I've removed the ECU control at pin 12 and joined the connections 12 and 14 together leaving pin 14 connection to the ECU only.

 

Restarting this thread. I am also finding that my AC runs continuously, regardless of whether or not the AC or Max AC buttons are activated. Problem seems to have started since I had my AC unit re-gassed a few weeks ago. My AC unit has been leaking as it was re-gassed 12 months ago and was out of gas once again. Now that it has been re-gassed, the AC runs all the time! Any ideas folks???

 

This may help:

 

The above diagram seems to suggest that the compressor's clutch electromagnetic coil is grounded on one side and fed + voltage from its relay to power it.

First of all a relay can be bad brand new so look at the electrical diagram and with the relay in your hand and test it with a volt ohm meter to make sure the proper pins that feed current to the clutch are electrically open when it is un-powered.

Then when you plug it in use a small tube as a stethoscope and see if you hear it actuate and if it does, does it do it immediately? A short to ground generally does not cause positive current to become available to a circuit however a bad grounding point can cause a positive current to feedback from another electrical device that shares the same grounding point to it.

If there is a delay in triggering look into other devices that trigger at the same time as the relay as this can lead you to where the the faulty shared ground is.

If you start pulling fuses one at a time to other circuits and it causes the relay to de-actuate this can be an indication of what devices' shared grounding point has been compromised. One of the electrical diagrams lists the locations of grounding points in the car.

Just some thoughts,
Andy

 

The wiring harness that controls the clutch is very delicate and runs right next to the ports that are used to regass the system. Look for a broken, pinched or damaged wire. Not sure how this may relate other than it is the only electrical part the technician should be anywhere near during recharging the system.

 

Thanks. That's an amazing amount of information! Prior to the re-gassing of the AC, the fans were running properly albeit blowing normal air rather than cooled. For instance, if I pressed Max AC, the fan speed would increase and I could hear the vents in the car closing for the window and feet and blasting air through the central vents.

The problem seems to have manifested since the re-gassing and I suspect your comment about the wiring harness that controls the clutch may be correct. This may have been disturbed during the re-gassing process and is now engaging the AC clutch continuously.

I will see what the technician thinks about this possibility.