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P0536A/C Evaporator Temperature Sensor Circuit Range/Performance

The A/C evaporator temperature sensor is producing a signal that is electrically valid but does not make sense compared to actual operating conditions.

Definition

The HVAC module or PCM performs rationality checks on the evaporator temperature sensor — for example, it should read close to ambient after a cold soak and should drop at a plausible rate once the compressor engages. P0536 sets when the reading is stuck, drifts, or fails to respond as expected even though the voltage is within range. Symptoms include compressor short-cycling, evaporator icing with gradually diminishing vent airflow, or reduced cooling; the fault is a comfort issue with no effect on how the engine runs.

Common causes

  • Drifted or lazy evaporator temperature sensor
  • Sensor probe pulled out of the evaporator fins, so it reads cabin air instead of core temperature
  • High resistance from corroded terminals or a poor splice skewing the reading
  • Evaporator airflow problems (plugged cabin filter, dirty core) creating implausible readings
  • HVAC module input fault (rare)

Common misdiagnoses

  • A/C compressor or compressor clutch
  • Expansion valve
  • Refrigerant charge adjustments
  • Blend door actuator

Troubleshooting steps

  1. 1.Compare to a known-good reference

    After overnight cold soak, the evaporator temp PID should agree with ambient and IAT within a few degrees; a large offset confirms drift.

  2. 2.Run the A/C and graph the PID

    The reading should fall smoothly into the 1-4 C range within a few minutes; a stuck or stair-stepping trace indicates a lazy sensor or bad connection.

  3. 3.Check sensor seating

    Verify the probe is fully engaged in the evaporator fins, especially after any evaporator, heater core, or dash service.

  4. 4.Measure circuit resistance

    Do a voltage-drop test on both sensor wires; anything more than about 0.1V of drop under load points to terminal or splice corrosion.

  5. 5.Replace the sensor if it drifts

    Confirm its resistance against the temperature chart at two temperatures; replace it if either point is out of specification.

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