GMC 2008 Sierra 1500 Pickup Owner's Manual page 164

To avoid blowing cold air in cold weather, the system
delays turning the fan on until warm air is available.
The length of delay depends on the engine coolant
temperature. Pressing the fan switch overrides this delay
and changes the fan to a selected speed.
O (On/Off): Press this button to turn off the climate
control system. Outside air still enters the vehicle,
and is directed to the floor. This direction can be
changed by pressing the mode button. Recirculation
can be selected once you have selected vent or bi-level
mode. The temperature can also be adjusted using
either temperature button. If the air delivery mode
or temperature settings are adjusted with the system off,
the display illuminates briefly to show the settings and
then returns to off. Press the on/off button or the up
down arrows on the fan switch, the defrost button,
AUTO button, or the air conditioning button to turn the
system on when it is off.
3-28
Manual Operation
The air delivery mode or fan speed can be manually
adjusted.
DC
(Fan): These buttons let you manually adjust the
D
fan speed. Press to increase fan speed and
to decrease fan speed.
Pressing either fan button while the system is off turns
the system on. Pressing either fan button while in
automatic control places the fan under manual control.
The fan setting remains displayed and the AUTO
light turns off. The air delivery mode remains under
automatic control.
HG H
(Mode): Press and
direction of the airflow in the vehicle. Repeatedly
press either button until the desired mode appears on
the display. Pressing either mode button while the
system is off changes the air delivery mode without
turning the system on. Pressing either mode button
while in automatic control places the mode under
manual control.
The air delivery mode setting is displayed and the
AUTO light turns off. The fan remains under automatic
control.
C
G
to manually change the