1. Perform the Diagnostic System Check - Vehicle before using the HVAC System Malfunction procedure in order to verify that all of the following are true:
• There are no DTCs set.
• The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to Automatic HVAC Description and Operation.

Note: Closing one or more outlets may adversely affect the operation of the Automatic HVAC system. Closed outlets reduce airflow and may negatively impact the ability of the system to maintain the desired settings. Where possible, always operate the system with all outlets open, and ensure non-adjustable outlets are unobstructed.

• Inspect for aftermarket devices which may affect the operation of the HVAC System.
• Inspect the easily accessible or visible system components for obvious damage or conditions which may cause the symptom.
• Verify that the customer is using the correct key to enable personalization and is not inadvertently activating auxiliary HVAC controls.
• The following conditions may cause window fogging:
• Wet carpet or mats
• High humidity
• Interior water leak
• Blocked A/C evaporator drain tube
• Maximum passenger capacity
• Blocked body pressure relief valves
• Inspect the air distribution system for causes of reduced air flow:
• Obstructed or dirty passenger compartment air filter, if equipped
• Blocked or damaged air inlet or outlet vents

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections.

Refer to HVAC System Malfunction in order to diagnose the symptom.