Technical Aircon not working

[SteveiC]

Yes, fuses and relays seem ok. I have a voltage probe/tester, that can send and receive voltages, so I'm confident the relays are good. The cable and switch I'm using can handle the current, as I already used them for something else, but is not for long term. Not using my MoHo for a few weeks, so I will check pin to pin and try to trace the issue.

has the A/C ever worked in your ownership, you said you'd had it topped up, surely the workshop that did that checked the system was working before they charged it up? Standard workshop practice is to fully empty the system, pressure test it that recharge with the correct weight of coolant...was yours done on a pressure reading?

See my earlie commeny about over charged systems, the compressor will not run if over or under pressure

 

[JohnBessacarr]

I've attached the description of the compressor wiring and function from elearn.

There's two fuses and two relays involved, T09 controlled by the ECU activates another relay T05 that activates the compressor solenoid.

It sounds like you got it working after bypassing T09 with a switch, which would indicate that the problem was somewhere on the ECU/sensor side (maybe F18 or T09 itself), or with the dashboard controls.

You will lose a few safety features controlled by the ECU:
- not engaging the compressor without sufficient gas pressure to prevent damage
- ditto if engine coolant is too hot

The ECU also disables AC under high acceleration, not sure if to protect it or to make all power available to the wheels.

Thanks for your advice. Yes, by passing T09, I believe the ECU and the pressure sensor is no longer in the loop, and using a mechanical switch on the T05 pins, the compressor is working, as a direct connection. I want to find the fault, so will checking pin to pin to trace the issue.