GMC Sierra Classic 2007 Owner's Manual page 235

When AUTO is selected, the air conditioning
operation and air inlet will be automatically
controlled. The air conditioning compressor will
run when the outside temperature is over
about 40°F (4°C). The air inlet will normally be
set to outside air. If it is hot outside, the air
inlet may automatically switch to recirculate
inside air to help quickly cool down your
vehicle. The light on the button will come on
in recirculation.
2. Set the driver's and passenger's temperature.
To find your comfort setting, start with a 74°F
(23°C) temperature setting and allow about
20 minutes for the system to regulate. Turn the
driver's or passenger's side temperature
knob to adjust the temperature setting
as necessary. If you choose the temperature
setting of 60°F (15°C) the system will
remain at the maximum cooling setting. If you
choose the temperature setting of 90°F
(32°C) the system will remain at the maximum
heat setting. Choosing either maximum
setting will not cause the vehicle to heat or
cool any faster.
Be careful not to cover the solar sensor
located on the top of the instrument panel
near the windshield. This sensor regulates air
temperature based on sun intensity. It also
turns on the headlamps. For more information
on the solar sensor, see "Sensors" later in
this section.
To avoid blowing cold air in cold weather, the
system will delay turning on the fan until
warm air is available. The length of delay
depends on the engine coolant temperature.
Pressing the fan switch will override this delay
and change the fan to a selected speed.
(Off): Press this button to turn off the entire
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climate control system. Outside air will still
enter the vehicle, and will be directed to the floor.
This direction can be changed by pressing the
mode button. The temperature can also be
adjusted using either temperature knob. Press the
up or down arrows on the fan switch, the defrost
button, the AUTO button, or the air conditioning
button to turn the system on when it is off.
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