HVAC System Malfunction

HVAC System Malfunction

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

Diagnostic Aids
Check the following mechanical fault sources:
- Air distribution box
- Air distribution hoses/air distribution ducts

Reference Information

Schematic Reference
HVAC Schematics [1][2]Electrical Diagrams

Connector End View Reference
Component Connector End Views

Description and Operation
Automatic HVAC Description and Operation Description and Operation

Electrical Information Reference
- Circuit Testing
- Connector Repairs
- Testing for Intermittent Conditions and Poor Connections
- Wiring Repairs

Scan Tool Reference
Control Module References for scan tool information

Circuit/System Verification

NOTE: Check for bulletins before proceeding.

1. Ignition ON, place the blower motor switch in each speed position. Verify that the blower motor operates properly in each position.
2. If the blower motor does not operate properly in all speeds, refer to DTC B0193.
3. Ignition ON, place the auxiliary blower motor switch in each speed position. Verify that the auxiliary blower motor operates properly in each position.
4. If the auxiliary blower motor does not operate properly in all speeds, refer to DTC B0208.
5. Using the scan tool observe the mode, temperature, air inlet and recirculation door positions. Verify the actual and commanded door positions are within 4 counts of each other.
6. If not within the specified range, refer to Circuit/System Testing DTC B0223, B022A, B0233, B023A, B0408, B0418, B0428, or B3531
7. Engine ON, A/C ON, place the temperature control in the coldest position. Verify that cool air flows from the ducts in the vehicle.
8. If the air is not cool, refer to Air Conditioning (A/C) System Performance Test
9. Turn the A/C OFF and place the temperature control in the warmest position.
10. If the air is insufficiently heated refer to Heating Performance Diagnostic.
11. Engine OFF, ignition ON, cover the sunload sensor assembly with a shop towel or other suitable item. Verify the scan tool Sunload Sensor parameter changes.
12. If it does not change, refer to Circuit/System Testing DTC B0163, B0183, or B1405.
13. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Passenger Compartment Air Temp. Sensor parameter. The measured temperature should be within 5 degrees of parameter.
14. If not within the specified range, refer to Circuit/System Testing DTC B0163, B0183, or B1405.
15. Measure actual temperature using a thermometer at each of the duct temperature sensors. Compare this value to the appropriate scan tool Duct parameter. The measured temperature should be within 5 degrees of appropriate Duct Temperature Sensor parameter.
16. If not within the specified range, refer to Circuit/System Testing DTC B0173, B0178, B0509, B0514, B0519, B3583, or B3933.
17. Ignition ON, observe the scan tool A/C Evaporator Temperature Sensor parameter. The reading should be between -39 °F (-35 °C) and 185 °F (85 °C) and change with evaporator air temperature changes.
18. If not within the specified range, refer to Circuit/System Testing DTC B0173, B0178, B0509, B0514, B0519, B3583, or B3933.

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

- HVAC Component Replacement Reference
- Control Module References for HVAC control module replacement, setup, and programming