Operation CHARM: Car repair manuals for everyone.
Home >> Chevrolet >> 2008 >> Cobalt L4-2.2L >> Repair and Diagnosis >> Heating and Air Conditioning >> Testing and Inspection >> Symptom Related Diagnostic Procedures >> Diagnosis By Symptom - HVAC System - Manual >> Air Temperature Malfunction

Air Temperature Malfunction



Air Temperature Malfunction

Diagnostic Instructions

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

Diagnostic Fault Information






Circuit/System Description

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of an electric motor and a potentiometer. The module supplies a low reference and 5-volt reference source voltage to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions.

Diagnostic Aids

Inspect the air temperature door and the air temperature actuator for the following conditions:

* A misaligned air temperature actuator
* Broken or binding linkages or air temperature door
* An obstruction that prevents the air temperature door from operating within its full range of motion
* Missing seals to the air temperature door
* Misaligned seals to the air temperature door

Circuit/System Verification

1. Ignition ON, place the blower motor switch at the maximum speed position and the mode switch in the vent or panel position.
2. Rotate the air temperature control switch from the full COLD position to the full HOT position. The air temperature should follow the commanded states of full HOT to full COLD through the vent or panel positions.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the air temperature actuator.
2. Test for less than 5 ohms between the low reference circuit terminal 7 and ground.

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

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 10 and ground.

• If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
• If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.

4. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 9 and ground.

• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
• If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.

5. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 5 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

6. Install a DMM between the actuator control circuit terminal 6 and ground. While monitoring the DMM, use the HVAC temperature control to command the appropriate actuator from one direction to the other. The voltage on the control circuit should move from 0 volts in one direction to 5 volts in the other direction and 2.5 volts in the at rest state.

• If the voltage does not change, test the control circuit for an open, short to voltage or short to ground. If circuit tests normal replace the HVAC control module.

7. If all circuits test normal, replace the air temperature actuator.

Repair Instructions

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

* Air Temperature Actuator Replacement
pro multis · About Operation CHARM