What are the symptoms of Hissing from vents and slow loss of refrigerant in Audi Allroad B9?

Weak cabin cooling. Hissing from vents. Musty mold odor from vents

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Hissing from vents and slow loss of refrigerant

Q: How to fix Hissing from vents and slow loss of refrigerant in Audi Allroad B9?

Replacing the air conditioning evaporator core, which involves comprehensive disassembly of the dashboard in the cabin, steering column and main console.

in Audi Allroad B9 (2017-2025)

Symptoms

Weak cabin cooling
Hissing from vents
Musty mold odor from vents

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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

A6 - (4FH) 2,7 TDI/3,0 TDI/3,2 FSI/4,2 FSI

Refrigerant: R134a Amount (g): 510 – 550g Oil: PAG PAO 68 lub PAG ISO 46 Oil (ml): 120 – 140ml

4BH

Refrigerant: R134a Amount (g): 750 – 850g Oil: PAG PAO 68 lub PAG ISO 46 Oil (ml): 240ml

See full specification

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