Mode Control Knob

A vacuum from the mode knob controls the doors in the heater module, which controls the airflow through the heater module. The mode knob positions are the following:
^ HTR
^ VENT
^ DEFROST

The intermediate positions are the following:
^ HTR
^ DEFROST
^ BLEND

When the mode knob is in the BLEND position, the controls are set to provide a combination of the features of the 2 nearest modes.