Chevrolet 2008 Silverado 1500 Pickup Owner's Manual page 212

Sensors
There is also an exterior temperature sensor located
behind the front grille. This sensor reads the outside
air temperature and helps maintain the temperature
inside the vehicle. Any cover on the front of the
vehicle could cause a false reading in the displayed
temperature on the rearview mirror.
3-34
The solar sensor, located
in the defrost grille, in the
middle of the instrument
panel, monitors the
solar radiation. Do not
cover the solar sensor or
the system will not
work properly.
The interior temperature
sensor, located in the
headliner, measures the
temperature of the air
inside the vehicle.
The climate control system uses the information from
these sensors to maintain your comfort setting by
adjusting the outlet temperature, fan speed, and the
air delivery mode. The system may also supply
cooler air to the side of the vehicle facing the sun.
The recirculation mode will also be used as needed to
maintain cool outlet temperatures.
Defogging and Defrosting
Fog on the inside of the 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. There are two modes to clear
fog or frost from the windshield.
H G
Use and to select the defog or defrost modes.
-
(Defog): Press this button to clear the windows of
fog or moisture and warm the passengers. This mode
directs air to the windshield, floor outlets, and side
window vents. When this mode is selected, the system
turns off recirculation and runs the air conditioning
compressor unless the outside temperature is close to
freezing. The recirculation mode cannot be selected
while in the defog mode. Do not drive the vehicle until all
the windows are clear.