Chevrolet 2002 Silverado 1500 Pickup Owner's Manual page 206

(Blend): Airflow is delivered through the floor
outlets, center floor console outlets (if equipped), the
windshield defroster outlets and the side window
defroster outlets. The air conditioning compressor may
run to dehumidify the air to prevent window fogging.
(Defrost): This setting directs most of the air
through the windshield defroster outlets, side window
defroster outlets and some air through the floor and
center floor console outlets (if equipped). If air from the
center floor console is not desired, or more defroster
performance is desired, turn the vents off at the
console. When in defrost mode, the air conditioning
compressor may run to dehumidifying the air and limit
window fogging.
(Outside Air): Press this button to direct the
system to use outside air.
Pressing the outside air button will cancel the
recirculation button.
3-4
(Recirculation): Press this button to limit the
amount of outside air entering the vehicle. This is
helpful when you are trying to limit odors entering the
vehicle or attempting to quickly cool down the interior.
Pressing recirculation will recirculate air continuously.
Recirculation is used when the fan is OFF to limit odors,
outside air and dust from entering your vehicle. All
button lights will go off. The last setting selected will
activate when the fan is turned back on.
Pressing the recirculation button will cancel the outside
air button. To return to normal operation and to prevent
stale air, be sure to return to outside air.
If the mode knob is placed between floor and blend
mode, outside air is forced to reduce window fogging.
If the recirculation button is pressed, the LED indicator
will flash three times indicating that forced outside air is
activated and recirculation is not available.