Global Machinery Company Sierra 1999 - Manual (Page 164)

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BLEND: Airflow is delivered through the heater
floor outlets, center floor console outlets (if equipped),
the windshield defroster outlets and the side window
defroster outlets. The air flow can be divided between
HEATER and DEFROST depending upon where the
knob is placed between the settings. 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 heater outlets
and center floor console outlets (if equipped). If air from
the center floor console outlets is not desired or more
defroster performance is desired, turn the vents off at the
console. When in the DEFROST mode, the air
conditioning compressor may run to dehumidify the air
to prevent 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.
RECIRCULATION: Press this button to limit
the amount of fresh outside air entering your vehicle.
This is helpful when you are trying to limit odors
entering your vehicle, because the air inside the vehicle
is being recirculated. Pressing RECIRCULATION will
recirculate air continuously.
RECIRCULATION is used when the fan control 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 blower is turned back on.
Pressing the RECIRCULATION button will cancel the
OUTSIDE AIR button.
In the 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.
The auto recirculation feature will activate when:
D the air conditioning system is activated,
D the OUTSIDE AIR button is on, and
D the vehicle load is high due to city traffic, extended
idling or hot weather.