What are the symptoms of Slow loss of refrigerant or A/C system leakage in Audi A4 (B9)?

No cold air from vents. Problem visible at standstill or in traffic

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Slow loss of refrigerant or A/C system leakage

Q: How to fix Slow loss of refrigerant or A/C system leakage in Audi A4 (B9)?

Replacing the sensor with a new, modified version (green dot on the housing, e.g. 4M0959603E, 4H0959126A, 4H0959126C) with a new O-ring. Replacement does NOT require sucking out the gas because there is a Schrader valve under the sensor. In case of a harness problem: cutting out the rotten wires in the chassis member and soldering new sections. The sensor can be replaced without sucking out the gas! The Schrader valve under the sensor protects the system. Saves the cost of operating the machine (~PLN 200-400). Green dot = corrected version.

in Audi A4 (B9) (2002-2023)

Symptoms

No cold air from vents
Problem visible at standstill or in traffic

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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Slow loss of refrigerant or A/C system leakage

Symptoms

DTC error codes

A/C Technical Specifications

Other problems in A4 (B9)

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