For 1990-2009 cars

Perform the Diagnostic System Check - Vehicle , prior to using this diagnostic procedure.

Important: The following steps must be completed before using the symptom tables.

1. Confirm the customer concern.

• | Review the service/repair history of the HVAC for prior work carried out.

• | Note the positions of the HVAC control settings.

• | Does the concern happen at certain speeds, rpm or length of driving?

2. Carry out Visual Inspection.

• | Broken, jammed or disconnected HVAC levers or gears.

• | HVAC case damage.

• | A/C system oil stains.

• | Noisy operating components.

• | Accessories blocking airflow.

• | Evidence of vehicle/component abuse.

• | Contamination, such as leaves in blower.

3. Check the battery voltage with a multimeter as the minimum voltage for the HVAC Control Module (HCM) operation is 9 volts and the maximum is 16 volts.
4. Take A/C System Pressure and Face Vent Temperature Readings.

• | Information to be used when diagnosing poor outlet temperature, either hot or cold.

• | A/C performance - Take readings at idle and at 2,000 rpm. Compressor High side pressure should increase at higher rpm.

5. Connect the Scan Tool.

• | Select appropriate vehicle and HVAC level.

• | Check that the HVAC is configured correctly for the vehicle. Refer to Instrument Cluster Programming and Setup .

6. Go to Function 1: Normal Mode - F1, F2, F3, F4. Check and Note any DTC’s both current and history for all modules.

Important: The HVAC control module receives and uses information from the other modules within the vehicle. This information is communicated via GMLAN. Poor performance of the GMLAN or another module can affect the function of the HVAC control module.

7. Go to F4: Miscellaneous Tests - F1 Switch Data. Carry out component activation via scan tool.

Important: This test will activate the component or function directly from the scan tool and if the component will activate during this test, but not by using the Infotainment facia. This will indicate a faulty Infotainment facia , GMLAN error, sub system module or wiring fault.