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Air Temperature Malfunction




Air Temperature Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

Diagnostic Fault Information





Circuit Description

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.

Reference Information
Schematic Reference

HVAC Schematics (HVAC - Automatic)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

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.

Circuit/System Testing

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.

Component Testing

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.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Ambient Air Temperature Sensor Replacement (Service and Repair)
* Inside Air Temperature Sensor Replacement (Service and Repair)
* Sun Load Temperature Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for HVAC control module replacement, setup, and programming

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