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Hissing from vents and slow loss of refrigerant

Q: What are the symptoms of Hissing from vents and slow loss of refrigerant in Multi-brand Niche Smart Fortwo/Forfour?

Frost or ice on pipes under the hood. Air conditioning does not turn on

Q: How to fix Hissing from vents and slow loss of refrigerant in Multi-brand Niche Smart Fortwo/Forfour?

LANCIA: Parts identical to Fiat/Alfa. SMART: Access to the compressor from the rear of the car (engine at the rear). LEXUS HYBRID: ONLY ND-11 (POE) oil - never PAG! CADILLAC: Diagnostics like GM + check GM service actions. LEXUS HYBRID = electric compressor = ND-11 MANDATORY. The same mistake as Toyota = cost of PLN 15,000+ disaster. Cadillac: check Special Coverage GM by VIN - free condenser replacement possible.

in Multi-brand Niche Smart Fortwo/Forfour (1998-2020)

Symptoms

Frost or ice on pipes under the hood
Air conditioning does not turn on

DTC error codes

Low pressure

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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

Refrigerant specifications for this model are available in the catalog.

Open refrigerant database

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