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!

[FLAPPERJACK76]

Do you have a shut-off code for the compressor?
What scan tool are you using?
From memory, go to 08 hvac ,measured value block 1 field value 1 and see what it says.

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[mc97riley]

I’m using OBDeleven. It’s the shut-off code 12

[FLAPPERJACK76]

Shut off by ecm via canbus, let me think on it. It's a bit early.

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[mc97riley]

Thanks mate I really appreciate it

[FLAPPERJACK76]

Any other faults anywhere else , mainly engine? Brakes?
I think.the ecu is reducing the load on the engine because there's either a temperature fault somewhere in hvac , or engine needs more vacumn. Can you see ac pressure readings in obd11.

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[FLAPPERJACK76]

Try measured value block 54 display 4

Display zone 4

Status of refrigerant pressure/temperature sender -G395.
The status is transmitted via the data bus system of the air conditioner LIN bus to the Climatronic control unit -J255.
J Readout = "0000XXXX" (breakdown)
Example
J Readout = "00000000" (no fault in refrigerant pressure/temperature sender -G395).
Breakdown of readout in display zone "4" of display group "054"
Allocation of possible fault types
J Readout = "0" (no fault)
J Readout = "1" (this fault detected)
Readout = "0000XXX1"
Measured value of installed pressure sensor faulty
Readout = "0000XX1X"
Measured value of installed temperature sensor faulty
Readout = "0000X1XX"
Fault in one of the two installed sensors or in the electronics
Readout = "00001XXX"
Fault in electronics of the refrigerant pressure/temperature sender -G395
Readout = "0000XXXX"
Red highlighted bits currently not used


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[mc97riley]

Hey mate, AC pressure reading is through the G65 sensor for this Golf (checks out fine) see attached screenshot.

Screenshot_20240412_134509_OBDeleven.jpg.

Somethinng that has piqued my interest however is the Radiator fan activation (Actual) vs (Specified). The specified in this screen shot is 36%. But there was no movement in the fans. Once the coolant temp rose to above 90 Degrees they then came on. What I think is happening is the HVAC is commanding the fans to come on with AC activation but maybe having a communication issue to the fan control module? The Engine control module is still able to command the fan control according to the engine temp annd cooling requirments? Possible fan control unit issue??

[FLAPPERJACK76]

Yes, could be, theres 2 small wires on fan yellow is ac activated by ac module, red is ecu, the fan controller is also inside the main fan, so if yellow is being pwm generated it could be the controller inside fan.

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[FLAPPERJACK76]

But there is probably a fuse as well for the fan inside e box by battery.

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