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.

Sunload Sensor Assembly

The sunload sensor is a 2-wire photo diode. Body ground and 5-volt signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. The sensor operates within an intensity range between completely dark and very bright. The sunload sensor provides the HVAC control module with a measurement of the amount of light shining on the vehicle. Bright or high intensity light causes the vehicles interior temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, cover the sunload sensor assembly with a shop towel or other suitable item. Verify the scan tool Right Sunload Sensor and Left Sunload Sensor parameters are within 3 counts of each other.

⇒	If not within the specified range, refer to Sunload Sensor Circuit Malfunction.

2. 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.

⇒	If not within the specified range, refer to Evaporator and Ambient Air Temperature Sensor Circuit Malfunction.

3. 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.

⇒	If not within the specified range, refer to Inside Air Temperature Sensor Circuit Malfunction.

4. 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.

⇒	If not within the specified range, refer to Evaporator and Ambient Air Temperature Sensor Circuit Malfunction.

Important: If any of the air temperature sensors or sunload sensors have an out of range condition caused by a short to voltage, short to ground, or an open/high resistance a diagnostic trouble code (DTC) will set. The following tests describe conditions that can cause inaccurate information to be processed in the HVAC control module and also operate between the minimum and maximum operating range without setting a DTC.

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 B.

•	Evaporator temperature sensor terminal 2.

⇒	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 B and the appropriate signal circuit terminal.

•	Ambient air temperature sensor terminal A.

•	Evaporator temperature sensor terminal 1.

⇒	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.

Sunload Sensor Circuit Malfunction

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

⇒	If greater than the specified range, test the ground circuit for high resistance.

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

•	Left sunload sensor circuit terminal A.

•	Right sunload sensor circuit terminal B.

⇒	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 sunload sensor.

Inside Air Temperature Sensor Circuit Malfunction

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

⇒	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 2 and the signal circuit terminal 1.

⇒	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 inside air 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.