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Unstable A/C operation in AUTO mode / incorrect cabin temperature

Q: What are the symptoms of Unstable A/C operation in AUTO mode / incorrect cabin temperature in Honda CR-V?

Unusual noises when A/C is turned on. Warning light on dashboard

Q: How to fix Unstable A/C operation in AUTO mode / incorrect cabin temperature in Honda CR-V?

Taking the car out of the garage into full sun and performing the air conditioning self-diagnosis again. In daylight, error B1421 disappears automatically. Do not replace the sensor if AUTO cooling is working properly.

in Honda CR-V (2000-2024)

Symptoms

Unusual noises when A/C is turned on
Warning light on dashboard

DTC error codes

DTC 21

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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

V - (RW)

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

See full specification

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Unstable A/C operation in AUTO mode / incorrect cabin temperature

Symptoms

DTC error codes

A/C Technical Specifications

Other problems in CR-V

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