GMC 2000 Savana - Manual (Page 144)

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A/C: Use for normal cooling on hot days. This setting
cools outside air and directs it through the instrument
panel outlets.
BI - LEVEL A/C: Use this setting to divide airflow
between the heater floor vents and instrument panel
vents. The air conditioning compressor may operate in
this setting to cool the air.
VENT: This setting directs air through the
instrument panel vents.
HEAT: This setting directs air through the heater
floor vents. This setting is useful for cold weather.
HEAT/DEFROST: Use this setting to divide
airflow between the heater floor vents and windshield.
DEFROST: This setting directs air through the
windshield defroster vents. This setting is useful when
you have fog or ice on the windshield.
Rear Heater (Without Air Conditioning)
If you have a rear heater (without rear air conditioning),
the control switch is located on the instrument panel.
To increase and decrease the flow of heated air to the
rear floor vents, turn the thumbwheel marked REAR
HEAT to the blower speed you want.
The knob has three speed positions. To increase the flow
of heated air, turn the thumbwheel toward HIGH. To
turn the fan off, turn the switch to OFF.