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P0535A/C Evaporator Temperature Sensor Circuit

There is an electrical fault in the A/C evaporator temperature sensor circuit, which the climate control system uses to keep the evaporator from freezing over.

Definition

The evaporator temperature (fin) sensor is a thermistor clipped into the evaporator core; the HVAC module or PCM reads it to cycle the A/C compressor off before the core drops below freezing and ices up. P0535 sets when the sensor voltage falls outside the valid range, indicating an open, short, or implausible signal. The system usually disables or restricts compressor operation as a protective default, so the main symptoms are weak or no A/C cooling, compressor short-cycling, or in some strategies evaporator freeze-up that chokes off vent airflow. There is no driveability impact, though the MIL can illuminate on some applications.

Common causes

  • Failed evaporator temperature sensor (open or shorted thermistor)
  • Damaged or chafed wiring under the dash near the HVAC case
  • Corroded or loose connector terminals at the sensor
  • Sensor dislodged from the evaporator fins after HVAC service
  • HVAC control module or PCM input fault (rare)

Common misdiagnoses

  • A/C compressor
  • Refrigerant recharge for an assumed low charge
  • Expansion valve or orifice tube
  • A/C pressure switch or pressure transducer

Troubleshooting steps

  1. 1.Read the evaporator temp PID

    After an overnight soak it should match ambient temperature within a few degrees; a pegged reading of -40 or +150 indicates an open or short.

  2. 2.Watch it with the A/C running

    The reading should fall steadily toward roughly 1-4 C (34-40 F) as the compressor runs; no movement means a sensor or placement problem.

  3. 3.Ohm-test the sensor

    Unplug it and compare resistance to the temperature chart in service data; as an NTC thermistor, resistance must drop smoothly as the sensor warms.

  4. 4.Inspect wiring and connector

    Check the pigtail at the evaporator housing for chafe, pin corrosion, and damage from previous dash or blend-door work.

  5. 5.Verify sensor placement

    Confirm the probe is fully inserted into the evaporator fins; a sensor hanging in the airstream reads warm and skews compressor cycling.

  6. 6.Replace the sensor

    If resistance is out of specification or the signal is erratic with good wiring, install a new evaporator temperature sensor and confirm normal cycling.

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