2000 GMC YUKON heater

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.

3-11 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.

3-12 Heating
The heater works best if you keep your windows
closed while using it. On cold days, use the HEATER
or VENT/HEAT setting with the temperature knob in
the red area.
On cold days, approximately 32
F (
-0
C) or lower, if
your vehicle is equipped with an automatic transmission,
you may experience differences in how the transmission
shifts until the engine is warm. This feature automatically
reduces the time it takes for the engine to reach normal
operating temperature and shortens the time it takes the
heater to reach full output.
If you use the engine coolant heater before starting your
engine in cold weather, 20
F (
-8
C) or lower, the
heating system will produce warmer air faster to heat the
passenger compartment.
The use of an engine coolant heater also reduces the
time it takes for the engine to reach normal operating
temperature. For more information, see ªEngine Coolant
Heaterº in the Index.
Defogging and Defrosting
On cool, humid days, use DEFOG to keep the
windshield and side windows clear. Use DEFROST to
remove fog or ice from the windshield in extremely
humid or cold conditions. Use DEFROST with the
temperature knob toward the red area and the fan
control turned all the way to the right.
Rear Window Defogger (If Equipped)
If you see lines running across the rear window, you
have a rear window defogger. The lines warm the glass.
To turn on the rear window
defogger, press this button
located next to the fan
control knob.
The rear window defogger
will only work if the
ignition is in RUN. For best
results, clear the window
of as much snow or ice
as possible first.

3-13
The defogger will shut itself off after several minutes.
If you need additional warming time, press the button
again. You can turn the defogger off at any time by
pressing the button.
If your vehicle is equipped with heated outside mirrors,
the rear window defogger button will also activate the
heated outside mirrors.
Do not attach a temporary vehicle license, tape or decals
across the defogger grid on the rear window.
NOTICE:
Don't use a razor blade or something else sharp
on the inside of the rear window. If you do, you
could cut or damage the warming grid, and the
repairs wouldn't be covered by your warranty.
Ventilation System
For mild outside temperatures when little heating or
cooling is needed, use VENT to direct outside air
through your vehicle. Air will flow through the
instrument panel outlets.
Your vehicle's ventilation system supplies outside air
to the inside of your vehicle when it is moving. With
the side windows closed, air will flow into the front
air inlet grilles, through the vehicle, and out the air
exhaust valves.
Outside air will also enter the vehicle when the heater
or the air conditioning fan is running, unless you have
the RECIRCULATION button pushed in. For more
information on the RECIRCULATION button,
see ªAir Conditioningº earlier in this section.

3-14
Your vehicle has air outlets
in the center and on the
sides of the instrument
panel and also may be
equipped on the headliner.
You can turn the outlets from side
-to-side or up
and down to direct the flow of air. The left driver
and passenger outlets on vehicles equipped with air
conditioning have shut off knobs. Turn the knob to
the left to shut off air flow, to the right to allow air flow.
When you close an outlet, it will increase the flow of air
coming out of any outlets that are open. The center
outlet does not completely shut off airflow.Ventilation Tips

Keep the hood and front air inlet free of ice, snow or
any other obstruction (such as leaves). The heater
and defroster will work far better, reducing the
chance of fogging the inside of your windows.

When you enter a vehicle in cold weather, turn the
blower fan all the way to the right for a few moments
before driving. This helps clear the intake ducts of
snow and moisture, and reduces the chance of
fogging the inside of your windows.

Keep the air path under the front seats clear of
objects. This helps air to circulate throughout
your vehicle.

The use of hood air deflectors may adversely
affect the performance of the heating and air
conditioning system.