GM Service Manual Online
For 1990-2009 cars only
Ventilation Mode: In the ventilation mode, air flows from the instrument panel (IP) outlets.

Bi-Level Mode: In the bi-level mode, airflow is divided between the IP air outlets and the floor air outlets. Warmer air is delivered to the floor air outlets than the IP air outlets.

Heat Mode: In the heat mode air flows from the floor air outlets, along with a small amount of air flow from the windshield defroster outlets.

Heat/Defroster Mode: In the heat/defroster mode, a portion of the airflow is from to the windshield defroster outlets while the remaining airflow is from the floor and side window air outlets.

Defrost Mode: In the defrost mode, most of the airflow is from the windshield defroster outlets. There is a small amount of airflow from the side window outlets and from the floor outlets.