Chevrolet 2002 Tahoe Owner's Manual page 187

(Defrost): This setting directs most of the air
through the windshield defroster outlets with air flow
also delivered from the side window and floor outlets.
When in defrost mode, the air conditioning compressor
may run to assist in dehumidifying the air and limit
window fogging.
Mode Buttons
(Outside Air): Press this button to force the
system to use outside air. Press is again to close off the
outside air.
Pressing the outside air button will cancel the
recirculation button.
(Recirculation): Press this button to limit the
amount of outside air entering your vehicle. This is
helpful when you are trying to limit odors entering your
vehicle or attempting to quickly cool down the interior.
Recirculation may be selected with the fan control in
OFF to limit odors, outside air and dust from entering
your vehicle.
Pressing the recirculation button will cancel the outside
air button.
A/C (Air Conditioning): Press this button to turn
the air conditioning on and off. The system will cool and
dehumidify the air inside the vehicle when the A/C light
is on. When in AUTO, the A/C is automatically engaged
when necessary.
Air conditioning will be automatically disabled when
the outside air temperature drops below a level at which
air conditioning is ineffective.
--
Mode Knob Automatic Operation
When the system is set for automatic operation,
sensors will control the air delivery mode. Air will
come primarily from the floor or instrument panel
outlets, with some air directed to the windshield to
prevent fogging.
When the system is in AUTO mode, the air conditioning
light will turn on, and the recirculation and outside air
lights turn off. With the system in full auto control
(both the fan and mode knobs in AUTO), you still have
the ability to override any function. However, continually
overriding the outside air or the A/C compressor will limit
the ability of the system to cool the vehicle quickly.
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