HVAC System Malfunction
HVAC System Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (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 (C68) (HVAC Schematics (C68))HVAC Schematics (CJ2) (HVAC Schematics (CJ2))
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Automatic HVAC Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) 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.
• If the blower motor does not operate properly in all speeds, refer to Circuit/System Testing DTC B0193 (B0193)
2. 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.
• If not within the specified range, refer to Circuit/System Testing DTC B0223, B022A, B0233, B023A, B0408, or B0418 (B0223)
3. Engine ON, A/C ON, place the temperature control in the coldest position. Verify that cool air flows from the ducts in the vehicle.
• If the air is not cool, refer to Air Conditioning (A/C) System Performance Test (Initial Inspection and Diagnostic Overview)
4. Turn the A/C OFF and place the temperature control in the warmest position.
• If the air is insufficiently heated refer to Defrosting Insufficient (Defrosting Insufficient)
5. 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.
• If it does not change, refer to Circuit/System Testing DTC B0163, B0183, or B1405 (B0163).
6. 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.
• If not within the specified range, refer to Circuit/System Testing DTC B0163, B0183, or B1405 (B0163).
7. 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.
• If not within the specified range, refer to Circuit/System Testing DTC B0173, B0178, B0509, B0514 or B3933 (B0173).
8. 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.
• If not within the specified range, refer to Circuit/System Testing DTC B0173, B0178, B0509, B0514 or B3933 (B0173).
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* HVAC Component Replacement Reference (Removal and Replacement)
* Control Module References (Programming and Relearning) for HVAC control module replacement, setup, and programming