System Purging: Notes
WARNING: This page is about a different car, the 2001 Pontiac Bonneville and 2000 Pontiac Bonneville. However, it is still accessible from the selected car via links, so may be relevant.
When A/C is turned on, A/C-heater programmer will purge stale air out of the system. When system is in AUTO mode, the A/C-heater programmer will determine if any undesirable conditions exist, and will choose one of 3 different purge modes to eliminate any undesirable conditions.