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.
Circuit/System Description
The heating and cooling system is controlled through the radio/HVAC controls faceplate interface. The HVAC control module receives a serial data message from the faceplate when the user chooses an HVAC function change. The HVAC module, hybrid powertrain control module 2, and engine control module (ECM) all interface via serial data and use inputs from air, refrigerant, coolant, and moisture temperature sensors, refrigerant pressure sensors, the sunload sensor, and the moisture sensors. This information is used to determine the optimal output for the passenger compartment coolant bypass valve, coolant heater, heater coolant pump, mode door, temperature door, recirculation door, and blower motor.
Diagnostic Aids
Check the following mechanical fault sources:
* Air distribution box
* Air distribution hoses/air distribution ducts
An HVAC door stepper motor control circuit fault may cause limited movement on one or all HVAC doors without setting codes. This could cause the following examples of customer concerns.
* Air from the HVAC ducts is either not cool or warm enough
* There is still some exhaust while in traffic or other outside air noticed when recirculation is requested
* Air does not flow from the correct ducts according to what bi-level mode has been chosen on the HVAC display
Reference Information
Schematic Reference
HVAC Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views Hybrid/EV Battery Pack X1
Description and Operation
Automatic HVAC Description and Operation HVAC - Automatic
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
1. Vehicle in Service Mode.
2. Verify the scan tool Blower Motor Switch parameter changes when pressing the switch
• If the parameter does not change
Replace the A20 radio/HVAC controls
• If the parameter changes
3. Verify that the blower motor operates properly with the blower motor switch in each speed position.
• If the blower motor does not operate in each speed position
Refer to DTC B0193 B0193.
• If the blower motor operates properly in each speed position.
4. Verify the scan tool parameters listed below change when pressing the appropriate switch.
* Left Temperature Switch
* Air Recirculation Mode Switch
* Bi-Level Switch
• If any parameter does not change
Replace the A20 radio/HVAC controls
• If all parameters change
5. Vehicle ON, HVAC in comfort mode.
6. Verify the HVAC modes listed below change when pressing the appropriate switch.
* Temperature
* Bi-Level Mode
* Recirculation
• If any HVAC mode does not change
Refer to DTC B0223, B0233, B023A, or B0408 B0223.
• If all HVAC modes change
7. Verify cool air flows from the ducts with the temperature control in the coldest position.
• If the air is not cool
Refer to Air Conditioning (A/C) System Performance Test Air Conditioning (A/C) System Performance Test.
• If the air is cool
8. Verify warm air flows from the ducts with the temperature control in the warmest position.
• If the air is not warm
Refer to Heating Performance Diagnostic Heating Performance Diagnostic.
• If the air is warm
9. Vehicle in Service Mode,
10. Verify the scan tool Sunload parameter changes, while covering the B10B ambient light sunload sensor with a shop towel or other suitable item.
• If the Sunload parameter does not change
Refer to DTC B0183 B0183.
• If the Sunload parameter changes
11. Verify the actual inside air temperature, using a thermometer, is less than 3°C (5°F) difference from the scan tool Inside Passenger Compartment Air Temperature parameter.
• If greater than a 3°C (5°F) difference
Refer to DTC B0163 B0163.
• If less than a 3°C (5°F) difference
12. Verify the scan tool parameters listed below are less than 3°C (5°F) of the actual duct temperature.
* Lower Left Duct Air Temperature
* Upper Left Duct Air Temperature
• If 3°C (5°F) or greater
Refer to DTC B0173, B0178, or B3933 B0173.
• If less than 3°C (5°F)
13. Vehicle ON and A/C ON.
14. Verify the scan tool A/C Evaporator Temperature parameter is between -35°C (-39°F) and 85°C (185°F) and changes as the evaporator air temperature changes.
• If the parameter is not between -35°C (-39°F) and 85°C (185°F)
Refer to DTC P0536-P0538 or P153B P0536.
• If the parameter is between -35°C (-39°F) and 85°C (185°F).
15. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* HVAC Component Replacement Reference HVAC Component Replacement Reference
* Control Module References Programming and Relearning for HVAC control module and radio/HVAC control replacement, programming and setup