GMC Sierra Classic 2007 Owner's Manual page 230

Mode Control
To change the current mode, select one of the
following:
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; then directs most
of the remaining air to the floor outlets. A little air
is directed toward the windshield and the side
window outlets. Cooler air is directed to the upper
outlets and warmer air to the floor outlets.
6
(Floor): This mode directs most of the air to
the floor outlets with a little air directed to the
windshield and the side window outlets.
230
h
(Recirculation): The recirculation mode is
used to recirculate the air inside of your vehicle.
Use this mode to help prevent outside odors and/or
dust from entering your vehicle or to help cool the
air inside of your vehicle more quickly. Press this
button to turn the recirculation mode on or off. The
light on the recirculation button will illuminate.
Recirculation cannot be used in floor, defog or
defrost modes. An indicator on the button will light
up, flash three times and turn off when recirculation
is selected in these modes. The air-conditioning
compressor will also come on when this mode is
activated. While in recirculation mode the windows
may fog when the weather is cold and damp. To
clear the fog, select either the defog or defrost
mode and increase fan speed.