Evaporator, Inside and Ambient Air Temperature Sensors

The HVAC control module supplies the evaporator, inside and ambient air temperature sensors with a low reference circuit and 5-volt signal circuit. The HVAC control module determines the voltage drop across the sensors, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Measure actual outside air temperature using a thermometer. Compare this value to the scan tool Outside Air Temp. Raw parameter. The measured temperature should be within 5 degrees of the parameter.
2. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. parameter. The measured temperature should be within 5 degrees of the parameter.
3. Measure actual evaporator air temperature using a thermometer. Compare this value to the scan tool A/C Evap. Temperature Sensor parameter. The measured temperature should be within 5 degrees of the parameter.

Evaporator and Ambient Air Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Ignition OFF, test for less than 10 ohms between the appropriate low reference circuit terminal and ground.

•	Ambient air temperature sensor terminal A.

•	Evaporator temperature sensor terminal A.

•	Inside air temperature sensor terminal B

⇒	If greater than the specified range, test the low reference circuit for high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal A and the appropriate signal circuit terminal.

•	Ambient air temperature sensor terminal B.

•	Evaporator temperature sensor terminal B.

•	Inside air temperature sensor terminal A

⇒	If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.

4. If all circuits test normal, test or replace the appropriate temperature sensor.

1. Test the appropriate air temperature sensor by varying the sensor temperature in water while monitoring the sensor resistance.
2. Compare the readings with the Temperature vs Resistance table and verify that the resistance is within 5 percent of the specification.

⇒	If not within the specified range, replace the sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.