Mode Lever
The mode lever controls the airflow air doors (defrost, heat and vent).
On setting the lever to the "VENT" position, air flows from the registers. Setting the lever to the "BI-LEVEL" position allows air flows to the registers, to the floor outlets and to the defroster outlets.
On moving the lever to the "HEAT" position, air flows to the floor outlets and to the defroster outlets. Moving the lever to the "DEFROST" position allows air to flow to the defroster outlets.