GMC 2008 Sierra 1500 Pickup Owner's Manual page 161

Temperature Control: Turn the center knob clockwise
or counterclockwise to increase or decrease the
temperature inside the vehicle.
Use the right knob to select from the following modes:
The right knob can be positioned between two modes to
select a combination of those two modes.
H
(Vent): This mode directs air to the instrument
panel outlets.
)
(Bi-Level): This mode directs half of the air to the
instrument panel outlets and to the floor outlets.
6
(Floor): This mode directs most of the air to the
floor outlets with some air directed to the windshield,
side window outlets, and second row floor outlets.
In this mode, the system will automatically select
outside air.
Defogging and Defrosting
Fog or frost on the inside of windows is a result of high
humidity (moisture) condensing on the cool window
glass. This can be minimized if the climate control
system is used properly.
Turn the right knob to select the defog or defrost mode.
-
(Defog): This mode clears the windows of fog or
moisture and warm the passengers. The air is directed
to the windshield, floor outlets, and side window vents.
0
(Defrost): This mode removes fog or frost from the
windshield more quickly. A portion of the air is directed
to the windshield and the side window vents, with
some air directed to the floor vents. The system will
automatically force outside air into the vehicle.
Do not drive the vehicle until all the windows are clear.
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