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

[mc97riley]

Thanks for the help mate! I've checked the continuity of all the fuses I could find (Engine compartment and inside the dash). Do you think I could just check to see if I am getting some sort of average voltage with this yellow wire coming from the AC control module when AC activated? If I am I'd assume there would be something going on with the fan control module inside the fan. Fingers crossed!

[FLAPPERJACK76]

Yes, probe into the yellow. See if getting anything there when ac is turned on, check the big cables as well for live and earth. The little red is when the engine is hot enough for normal cooling fan operation.

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[Crasher]

The way we look at it is "no codes, good pressure, new compressor"

[FLAPPERJACK76]

You're probably right Crasher, we were told check ac output in mvbs when you get something like 4nm no point going further

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[mc97riley]

Yeah at this point I’m thinking of just replacing the AC compressor. But I’m not the biggest fan of throwing parts at it. But at this point I haven’t got any other choice :/

[Crasher]

We only fit Denso to replace the unreliable Sanden which is normally fitted.

[mc97riley]

Thanks for your help guys, I'll most likely buy a new compressor annd cross my fingers.

It appears a similar issue with the same symptoms in this thread was solved by replacing his compressor.
[1.6 FSI Climate control + ECU Compressor Intervention] | Audi A2 Owners' Club

I guess even though I hard wired the solenoid to manually bypass the ECM and had apparent cold air come out of the system, maybe my compressor is still going bad. My Question is how does the ECM know this an is able to shut it down? Can it detect an abnormally high load coming from the compressor?

[mc97riley]

Are you able to shed some light on what it feels like to rotate a compressor going bad? I've taken the belt off of mine and it rotates with ease very smoothly. I've attached a known working N280 solenoid to the harness hanging externally to the compressor (Old one still installed so I don't loose refrigerant while trying to troubleshoot). In my mind it just cannot be the compressor that's causing the ECM to spit out the compressor code 12. I'm 80% sure that replacing these expensive parts is going to be pointless.

I'm leaning on something like the fan control unit? Even though doing an output test works fine though OBDeleven. Maybe there's miscommunication between that and the environmental control unit (J255)??

And Finally 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...