Ventilation System - GMC C-Series 2001 Owner's Manual

Defogging
Use DEFOG, along with the HEATER setting, when
there is fog or ice on the windshield. This will direct
airflow toward the windshield and front side windows.
Set the temperature selector toward "H" and the
fan control at a comfortable level. When the windshield
is clear, use the temperature selector bar and the
fan control button to maintain a comfortable
temperature level.
3-6

Ventilation System

Air comes into your vehicle in one of two ways: power
air or ram air. Power air means bringing outside air into
the cab through the air intake, using the blower fan.
Fresh air can be drawn in when the vehicle is stationary
or moving at low speed. Air comes in through four vents
in the instrument panel and is exhausted through the
vents and pressure relief valves in the doors and door
pillars. Power ventilation means an increased supply
of fresh air is brought into the cab interior without
having to open the windows, especially during
inclement weather.
Ram air is forced into the cab through the air intake in
the cowl by the vehicle's forward motion. This air is
controlled by two vent air handles under the instrument
panel. Air is directed through the ventilation ducts to the
floor. Ram air provides good airflow into the cab at
normal road speeds.