Planning the next
AO Silver Member
Join Date: May 2007
Location: United Kingdom
Great, that's narrowed it down to just what I need. That means you should have the M2.10.4 engine ECU.
In the engine bay, you'll have relay Q22. Probably with the other relays in the black box on the bulkhead. 4 wirer : Red, Brown, Orange and Brown/Black.
With the ignition on, short the Brown/Black wire to earth. If all is well, the compressor clutch will engage and that should prove the relay and engine bay compressor wiring is OK.
If the compressor clucth doesn't engage, you need to test the red wire for +12v ( permanent ) and the orange wire for +12v ( ignition on ). If they're OK, you either have a problem with the brown wire to the compressor or the relay has failed.
If all is well so far, the next most likely point of failure are the pressure switches.
There are two switches near the air filter housing located in the air con pipes. One has two wires both Green/White. Disconnect the connector and test the switch for connectivity. If the pressure switch is shorted, that's good. It's telling the engine ECU that there is enough refrigerant. If the switch is open circuit either the switch has failed or there is insufficient refrigerant pressure. If it is open circuit, start the car and let it run for a minute and short out the two Green/White wires at the connector. If the compressor engages, it confirms low pressure/faulty switch. Don't leave it shorted for more than a few seconds in case it is low refrigerant pressure.
The other switch has at least 4 wires ( Green/white, green, grey/black, black ). This stops the compressor working if there is too much refrigerant pressure. The green & green/white wire terminals should be shorted if the switch is working and refrigerant pressure isn't too high. If the switch is open circuit, you either have too much refrigerant pressure or the switch is broken. Again, it can be tested : with the engine running for a minute, short the green & green/white wires at the connector. The compressor should engage. Again, don't short it out for more than a second or two! Tghe other wires on this switch are related to the engine cooling fans and wouldn't prevent the compressor engaging.
There are other things that could have failed but that covers the most likely points.