GMC 1999 Suburban Owner's Manual page 155

Heater and Air Conditioning Control
System (If Equipped)
Fan Knob
The knob on the left side of the heating system control
panel controls the fan speed. The knob has four speed
positions. To increase airflow, move the knob toward
HI. To decrease airflow, move it toward LO. To turn the
fan off, move the knob to OFF. If you have the air
conditioner on, moving the fan knob to OFF also turns
off the A/C compressor.
While driving with the fan knob in OFF, ram airflow
will vent to the floor outlets. The mode knob will not
redirect ram airflow to other selected outlet positions.
This is a normal operation for the OFF position.
Temperature Knob
The middle knob on the control panel lets you select the
relative temperature of the air flowing into the passenger
area of your vehicle. This knob will allow you to adjust
the relative air temperature independently of the
function knob setting. Move the knob clockwise to the
red area for warmer air. Move the knob
counterclockwise to the blue area for cooler air.
Mode Knob
The right knob on the control panel allows you to
choose the direction of air delivery. The control knob
can be placed in any position between any two mode
settings to blend the flow of air.
VENT: This setting directs air through the
instrument panel outlets.
VENT/HEAT: Use this setting to divide airflow
between the floor outlets and instrument panel outlets.
HEATER: This setting directs air through the
floor outlets.
DEFOG: This setting directs air to the heater
outlets and toward the windshield.
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