1999 GMC SUBURBAN Owner's Manual

3-4
DEFROST: This setting directs most of the air
through the windshield defroster outlets, side window
defroster outlets and some air through the heater outlets.
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. This is the setting which
should be used for normal operation.
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 or attempting to quickly cool
down the interior. 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. To return to normal
operation and to prevent stale air, be sure to return
to OUTSIDE AIR.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 and
RECIRCULATION is not available.
The auto recirculation feature will activate when:

the air conditioning system is activated,

the OUTSIDE AIR button is on, and

the vehicle load is high due to city traffic, extended
idling or hot weather.
The system will automatically switch to the recirculation
mode to lower the system load and improve interior
comfort. The OUTSIDE AIR and RECIRCULATION
button LEDs will not change. The system will return
to the OUTSIDE AIR function when the system load
is reduced.
A/C: 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.
Air conditioning will be automatically disabled when
the outside temperature drops below a level at which
air conditioning is effective.

3-5 Electronic Climate Control System
(If Equipped)
Fan Control
The knob on the left side of the electronic climate
control panel controls the fan speed. To manually
increase airflow, move the knob clockwise. To manually
decrease airflow, move it counterclockwise.
OFF: If the knob is in OFF, outside air will still enter
the vehicle, and will be directed based on the position of
the mode knob.
AUTO: If the knob is in AUTO, the fan speed will vary
as the system maintains the selected temperature.When both the Fan Control and Mode Knobs are in
the AUTO position, the system will then automatically
maintain the desired cabin temperature as selected by
Temperature Knob. Manual control of functions is
also available.
Temperature Knob
The middle knob on the control panel lets you select
the desired air temperature in your vehicle. This knob
will allow you to adjust the interior air temperature
independent of the function knob setting. Move the
knob clockwise toward 82 for warmer air. Move the
knob counterclockwise toward 66 for cooler air. When
the system is set for automatic operation, sensors will
control the fan/blower speed.
Full Hot: If you turn the temperature knob past
82
F (28
C), the system will go into the ªfull hotº
mode. The system will remain at that maximum heating
setting and the fan will blow at the speed the fan knob is
set to. If the fan is in AUTO, it will run at full speed.
Full Cold: If you turn the temperature knob past
66
F (19
C), the system will go into the ªfull coldº
mode. The system will remain at that maximum cooling
setting and the fan will blow at the speed the fan knob is
set to. If the fan is in AUTO, it will run at full speed.

3-6
Mode Knob - Automatic Operation
The right knob on the control panel allows you to
choose the direction of air delivery. 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.
If you push a button for a function which is not
available, the light next to that button will flash three
times to alert you that it's not available.
To find your comfort zone, start with the 74
F (23
C)
setting and allow about 20 minutes for the system to
adjust the temperature if necessary.With the automatic setting, the air conditioning
compressor automatically cycles when needed to cool the
air. In cold weather, when the system senses the need
for heat, the airflow will be directed out the floor outlets.
As the interior temperature approaches a desired setting,
the blower speed will decrease. To maintain interior
comfort, the airflow will adjust between the instrument
panel air outlets and floor outlets. On bright sunny days
in cool weather, the airflow may come out of the air
conditioning and floor outlets (bi
-level mode) to maintain
comfort and prevent stuffiness.
To avoid blowing cold air in cold weather, the system
will delay turning on the fan until warm air is available.
The length of delay depends on the outside air
temperature, engine coolant temperature or the time
since the engine was last started. As the coolant warms
up, the blower fan speed will gradually increase and
air will flow from the heater outlets, with some airflow
to the windshield to prevent fogging under most
normal conditions.
Be careful not to put anything over the solar sensor
located around the center of the instrument panel.
This sensor is used by the automatic system to
regulate temperature.

3-7
Mode Knob - Manual Operation
The right knob on the control panel allows you to
choose the direction of air delivery.
You can choose to set the climate control system
operations yourself, or let the system work for you
by placing the system in AUTO mode. See ªMode
Knob
- Automatic Operationº earlier in this section.
PANEL: This setting directs most of the air
through the instrument panel outlets and a small amount
through the floor outlets.
BI-LEVEL: Air is delivered through the heater
floor outlets as well as the instrument panel outlets.
HEATER: This setting directs most of the
warmed air through the heater floor outlets and some
air through the windshield defroster outlets.
BLEND: Airflow is divided equally between the
heater floor outlet and the windshield defroster outlets.
The air conditioning compressor may run to dehumidify
the air to prevent window fogging.
DEFROST: This setting directs most air through
the windshield defroster outlets and some through the
heater outlets. The air conditioning compressor may
run to dehumidify the air to prevent window fogging.
OUTSIDE AIR: Press this button to force
the system to use outside air. Press it 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 fresh 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.
In the AUTO mode, the system will use recirculation
as necessary to cool the air. Pressing the recirculation
button will change the operation to a manual mode and
the air will recirculate non
-stop. Press this button again
to turn off the recirculation feature.
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: 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.

3-8
Air conditioning will be automatically disabled when
the outside temperature drops below a level which air
conditioning is ineffective.
Remember that in order for the automatic system to perform
well, it needs A/C to provide cooling performance.
Rear Air Conditioning and Heating Systems
(If Equipped)
If your vehicle has one of these systems, you can increase
and decrease the airflow at the rear vents. Depending on
the system you have and the setting selected, you can
send cooled or heated air to the rear of the vehicle.
Rear Air Conditioning (Without Rear Heater)
(If Equipped)
To increase and decrease the flow of cooled air to the rear
vents, turn the rotary knob to the blower speed you want.
The knob has three speed positions. To increase the flow
of cooled air, turn the switch toward 3. To decrease the
flow of cooled air, turn it toward 1. To turn the fan off,
turn the knob to OFF.
To operate the rear system using the front control,
just turn the knob to the blower position you want.
To use the rear control, first turn the front control knob
to REAR. Then, the rear control can be used to increase
and decrease the airflow.

3-9
Rear Air Conditioning and Rear Heater
(If Equipped)
If your vehicle has the rear air conditioning and rear
heater system combination, controls are provided to
regulate temperature, location and speed of the airflow.
Front Control
To adjust the airflow speed, turn the fan control knob
located on the left side to the desired blower setting.
To activate the second seat control system, turn the fan
knob on the front overhead control to REAR.
To regulate the airflow location, adjust the right knob on
the control panel. Turn the knob clockwise for floor vent
airflow or counterclockwise for headliner vent airflow.Generally, the upper vents are used for air conditioning
and the floor vents for heating. The control knob can be
set to any blend setting.
To adjust the air temperature, turn the temperature knob
on the center of the control panel.
For warmer air, turn the knob clockwise toward the red,
and for cooler air, turn the knob counterclockwise.
Rear Control
The rear control works just like the front control. It will
allow second seat passengers to adjust the controls as
they desire. To use the rear control, first turn the front
control knob to REAR.

3-10 Rear Air Conditioning and Heating Systems
with Electronic Climate Control System
(If Equipped)
Front Control
Rear ControlWith this system the rear passengers can control the
temperature of the air flow for his/her own zones.
The climate control has three controls.
To adjust the airflow speed, turn the fan control knob
located on the left side of the control panel to the desired
blower setting.
The system also has a front AUTO setting that can
automatically change the temperature of the rear seating
area based on information from the front control. An
OFF setting, located on the front climate control panel,
also allows the driver to turn off the rear passenger seat
controls from the front seat.
To adjust the air temperature, turn the temperature knob
on the center of the control panel.
For warmer air, turn the knob clockwise toward the red.
Turn the knob counterclockwise toward the blue for
cooler air.
To regulate the airflow location, adjust the right knob on
the control panel. Turn the knob clockwise for floor vent
airflow or counterclockwise for headliner vent airflow.
Generally, the upper vents are used for air conditioning
and the floor vents for heating. The control knob can be
set to any blend setting.
For rear control operation, use the above instructions.

3-11 Air Conditioning
On hot days, open the windows long enough to let hot
air inside escape. This reduces the time it takes for your
vehicle to cool down. Then keep your windows closed
for the air conditioner to work its best.
The RECIRCULATION button allows the air inside
your vehicle to be recirculated. This setting helps to
maximize your air conditioner's performance and your
vehicle's fuel economy. This setting also cools air the
fastest and can be used to keep unwanted odors
and/or dust from entering the vehicle. When using
the air conditioner, turn off the RECIRCULATION
button after the vehicle reaches a comfortable interior
temperature. When the right knob on the control panel
is between HEATER and DEFROST, the recirculation
feature will not function to reduce window fogging.The A/C button, below the mode knob, allows the air
coming into your vehicle to be cooled. This setting is
useful for normal cooling on hot days. When you use
A/C with the RECIRCULATION button pushed in,
turn off recirculation as soon as the vehicle reaches a
comfortable interior temperature.
Maximum air conditioning performance is obtained by
pressing the A/C button, the RECIRCULATION button
and turning the temperature knob fully counterclockwise
to the blue area. This setting also cools air the fastest.
After the vehicle's interior reaches a comfortable
temperature, press the OUTSIDE AIR button to
place the air conditioning system in the normal mode.
Passenger Compartment Air Filter (If Equipped)
If your vehicle has air conditioning, it is equipped
with a passenger compartment air filter, which filters
outside air entering the vehicle. For information on
replacing the filter see ªPassenger Compartment
Air Filterº in the Index.