Intermittent Poor AC Performance Or Vapor From Vents - keywords A/C ac air blower compressor condition core evaporator freeze hot HVAC sensor temperature

This PI was superseded to update Recommendation/Instructions. Please discard PIT4456.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

If the customer complains that A/C performance is poor or not cold enough, with symptoms such as blowing warm air, reduced air flow, or mist/vapor coming out of the vents, the likely fault is an evaporator core freezing up.

This is a common problem with air conditioning when using a low blower speed at ambient temperatures in the mid 70°F and high humidity levels.

1. Check for current and history DTCs - address DTCs prior to further diagnosis.
2. Assure sufficient air flow through the HVAC system - Select high blower speed and direct airflow to the IP. Evaluate air flow volume in both 'fresh air' and 'recirculation' modes. If there is noticeably less airflow than a known-good vehicle, repeat this evaluation after 30 minutes with the engine off. If airflow is restored after 30 minutes, the restriction is likely due to evaporator freeze - continue with this information. If airflow is not restored, inspect the intake plenum for blockage.
3. Recalibrate the HVAC control module with the appropriate latest calibration.

The following HVAC calibration part numbers have been released to service to correct this issue.

Notice: It is important to always use the correct operating system and calibration files when programming a HVAC System. Never use an operating system or calibration file intended for another RPO in an attempt to resolve a concern. Using an incorrect file may result in permanent damage. To select the correct operating system or calibration file, first determine the RPO (C67 or C68).

2008

C68:

25845399 - HVAC OPERATING SYS

25845400 - HVAC SYS CALN

25904459 - HVAC AIRFLOW CALN

C67:

25863337 - HVAC OPERATING SYS

25863336 - HVAC SYS CALN

25904460 - HVAC AIRFLOW CALN

If the vehicle was built after June 23, 2007 or if the above calibration is already in the vehicle, then follow the normal diagnostic procedures.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.