What are the symptoms of Air conditioning stopped cooling / no response to AC button in Audi A4 (B7)?

Different temperature on both sides of the cabin. A/C does not react to control panel settings

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Air conditioning stopped cooling / no response to AC button

Q: How to fix Air conditioning stopped cooling / no response to AC button in Audi A4 (B7)?

Physical replacement of the J255 controller (used or new) and rigorous coding in VCDS/OBDeleven. Without coding, the new unit will not read the car's components correctly. Before purchasing a new J255, check the part number exactly according to the equipment (heated seats yes/no changes the number!). Used from the same model, it can be coded without visiting the dealer - all you need is VCDS and knowledge of the original coding.

in Audi A4 (B7) (2001-2011)

Symptoms

Different temperature on both sides of the cabin
A/C does not react to control panel settings

DTC error codes

00819

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Technical diagnosis (Premium)

Recognized technical fault:

Auxiliary controller voltage instability detected

Technical analysis

Detailed analysis of HVAC controller operation parameters, CAN bus data readings, and diagnostic signal waveforms. Purchase PRO access or log in to read the full fault analysis.

Confirmed solution

Complete step-by-step repair procedure including module non-volatile memory reset, sensor calibration, and correct wiring routing. Unlock the full report to see the instruction.

Parts needed

Filters ferrite anti-interference / noise suppressor
Auxiliary starting battery (depending on cell status)

Workshop hacks

Important workshop tips for mechanics regarding bypasses without expensive control module replacement and manufacturer software service bulletins.

TSB / TPI service bulletins

TSB-24-HVAC-01TPI-2068943/2

A/C Technical Specifications

(B9)

Refrigerant: R1234yf Amount (g): 580g Oil: PAG ISO 46 YF Oil (ml): 110ml

(B9)

Refrigerant: R1234yf Amount (g): 480-530g Oil: PAG YF ISO 46 Oil (ml): 120 - 150ml

S4 / RS4 (B9) - Wersje z czynnikiem R134a (590g) oraz R1234yf (525g)

Refrigerant: R134a / R1234yf Amount (g): 525 / 590 ±15g Oil: ND-12 / SP-A2 / PAG46yf Oil (ml): 100 / 110ml

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Air conditioning stopped cooling / no response to AC button

Symptoms

DTC error codes

A/C Technical Specifications

Other problems in A4 (B7)

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