Chevrolet Silverado Classic 2007 Owner's Manual page 230

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.
Temperature Control
Driver's Side: The lever on the left side of the
climate control panel is used to raise or lower the
temperature on the driver's side of the vehicle.
This lever also adjusts the temperature to
the center console outlets, if the vehicle has them.
Passenger's Side: The lever on the right side
of the climate control panel is used to raise
or lower the temperature on the passenger's side
of the vehicle.
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(Air Conditioning): Press this button to
turn the air-conditioning system on or off. When
the button is pressed, an indicator light will
come on and the system will begin to cool and
dehumidify the air inside of your vehicle. You may
notice a slight change in engine performance
when the air conditioning compressor shuts off
and turns on again. This is normal.
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 choose from to clear fog or frost
from your windshield. Use the defog mode to clear
the windows of fog or moisture and warm the
passengers. Use the defrost mode to remove
fog or frost from the windshield more quickly.