AC Issue, Compressor Shut-off From ECM (Code 12)

[mc97riley]

I've been banging my head against a wall with this one. Ever since owning my 2008 Mk5 1.9L TDI Golf. I've never been able to figure out why the AC does not blow cold air. More specifically why the ECM is commanding the compressor to not engage.

I've scanned the car and there are no faults in the Engine or HVAC Module, All the sensors are working and reading within expected range (Replaced the N280 annd G65) No leaks in the AC System and been Regased.

Compressor and Radiatior fans confirmed working after manually bypassing the ECM and engaging the N280 Solenoid / hard wiring the fans; cold air came out. Fuses checked.

So I'm 99% sure the ECM is receiving something it's not happy about and is to my understanding "load shedding" systems. But unfortunately I haven't been able to find any information as to what causes it to spit the dummy! Other than a possible vacuum leak in the brake system. But I have isolated that and believe there's no issue there. again nothing found on live scans through OBDeleven.

I've literally searched for hours and hours going the SSP's, Wiring diagrams, Forums and random youtube vidoes spoken in russian trying to get to the bottom of it. Can someone please help!

Thank you!

[JustCruisn]

The compressor is probably blown. Mine never gave any codes, but a new compressor resolved it.

[mc97riley]

Thanks for the reply mate. Was your compressor seized and hard to rotate when replaced? I took the belt off of mine and it spins freely. I just don't understand how the ECM knows to shutdown the system and throws out the compressor shutoff code 12 instantaneously when the AC button is pressed. I really feel like there is a wiring issue that isn't showing up?

[mc97riley]

Furthermore i've found this in the 1.9L TDI SSP from VW:

Air conditioner compressor cut-off To reduce engine load, the engine control unit switches theair conditioner compressor off in the following conditions:
- after every starting cycle (for approx. 6 seconds)
- under rapid acceleration from the bottom end of the revband
- at coolant temperatures in excess of +120°C
- in the emergency running program.

The investigation and head banging continues...