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A/C cooling is weak and gradually loses performance

Q: How to fix A/C cooling is weak and gradually loses performance in Toyota Highlander?

Replacing the M/G CLT (Magnetic Clutch) relay with a new, updated revision (Toyota has released a new, revised relay: 90987-02028 / Denso 156700-3290). If the AC diode is flashing, it does not mean a burned clutch or lack of gas. Replace the M/G CLT relay with another one from the same box (e.g. HORN). If the air conditioning starts and the LED stops flashing, you have a solution. It is mandatory to use the corrected part with the number ending '028', the older version '022' is factory defective.

in Toyota Highlander (2001-2012)

Symptoms

Weak cabin cooling

DTC error codes

Fault in A/C module (B1422 - Compressor Lock Sensor)

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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

Standard

Refrigerant: R134a Amount (g): 820g Oil: ND8 PAO 68 AA1 lub PAG ISO 46 b.d. Ipsum Oil (ml): 1996 – 01ml

Standard

Refrigerant: R134a Amount (g): 750g Oil: ND8 PAO 68 AA1 lub PAG ISO 46 b.d. Oil (ml): b.d.ml

See full specification

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A/C cooling is weak and gradually loses performance

Symptoms

DTC error codes

A/C Technical Specifications

Other problems in Highlander

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