1999 GMC SIERRA heating

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2-58 Rear Ashtray (If Equipped)
To use a rear ashtray, if you have them, pull at the top of
the ashtray door to flip the door open.
To remove a rear ashtray, press down on the inside tabs
and open the door fully.
NOTICE:
If you store paper or other things that burn in
your ashtrays, they could be set on fire by
cigarettes or other smoking materials. That could
cause a fire and possibly damage your vehicle. Do
not store papers and other things that burn in
your ashtrays.
To use the cigarette lighter, push it in all the way and let
go. When it's ready, it will pop back by itself.
NOTICE:
Holding a cigarette lighter in with your hand
while it is heating can make it overload,
damaging the lighter and the heating element.
Just push the lighter all the way in and let go.
When it's done, it will pop back by itself.

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2-69 Anti-Lock Brake System Warning Light
With the anti-lock brake
system, this light will come
on when you start your
engine and may stay on
for several seconds.
That's normal.
If the light stays on, or comes on when you're driving,
your vehicle needs service. If the regular brake system
warning light isn't on, you still have brakes, but you
don't have anti
-lock brakes. If the regular brake system
warning light is also on, you don't have anti
-lock brakes
and there's a problem with your regular brakes. See
ªBrake System Warning Lightº earlier in this section.
The anti
-lock brake system warning light should come
on briefly when you turn the ignition key to RUN. If the
light doesn't come on then, have it fixed so it will be
ready to warn you if there is a problem.
Engine Coolant Temperature Gage
This gage shows the engine
coolant temperature.
It also provides an indicator of how hard your vehicle is
working. During a majority of the operation, the gage
will read 210
F (100
C) or less. If you are pulling a
load or going up hills, it is normal for the temperature to
fluctuate and approach the 260
F (125
C) mark. If the
gage reaches the 260
F (125
C) mark, it indicates that
the cooling system is working beyond its capacity.
The ªProblems on the Road,º section of this manual
shows what to do. See ªEngine Overheatingº in
the Index.

3-
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3-1
Section 3 Comfort Controls and Audio Systems
In this section, you'll find out how to operate the comfort control and audio systems offered with your vehicle.
Be sure to read about the particular systems supplied with your vehicle.
3
-2 Comfort Controls
3
-4 Air Conditioning
3
-4 Heating
3
-5 Ventilation System
3
-6 Defogging and Defrosting
3
-6 Rear Window Defogger (If Equipped)
3
-7 Audio Systems
3
-7 Setting the Clock
3
-8AM-FM Stereo
3
-8 Playing the Radio
3
-10 AM-FM Stereo with Cassette Tape Player
(If Equipped)3
-12 AM-FM Stereo with Cassette Tape and
Automatic Tone Control (If Equipped)
3
-16 CD Adapter Kits
3
-17 AM-FM Stereo with Compact Disc Player and
Automatic Tone Control (If Equipped)
3
-21 Remote Compact Disc Player (If Equipped)
3
-22 Theft-Deterrent Feature (If Equipped)
3
-24 Understanding Radio Reception
3
-25 Tips About Your Audio System
3
-26 Care of Your Cassette Tape Player
3
-27 Care of Your Compact Discs
3
-27 Care of Your Compact Disc Player
3
-27 Fixed Mast Antenna

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3-2
Comfort Controls
Heater Control System
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, turn the knob toward HI.
To decrease airflow, turn it toward LO. To turn the fan
off, turn the knob to OFF.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. Turn the knob clockwise, toward the red
area, for warmer air. Turn the knob counterclockwise,
toward 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 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.
DEFROST: This setting directs air toward
the windshield.

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3-3 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, turn the knob toward HI.
To decrease airflow, turn it toward LO. To turn the fan
off, turn the knob to OFF. If you have the air conditioner
on, turning the fan knob to OFF also turns off the
A/C compressor.
In OFF, while driving, ram airflow will vent to the floor
outlets. The mode knob will not redirect ram airflow to
other selected outlet positions. This is 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. Turn the knob clockwise, toward the red
area, for warmer air. Turn the knob counterclockwise,
toward 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 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
heater floor outlets.
DEFOG: This setting directs air to the heater
outlets and toward the windshield.
DEFROST: This setting directs air toward
the windshield.

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3-4 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, between the fan and
temperature knobs, 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 the 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 recirculation 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.
The A/C button, between the temperature and mode
knobs, 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.With the A/C on, turn the temperature knob to MAX for
maximum cooling. This setting also puts the system in
the recirculation mode and helps to maximize your air
conditioner's performance and your vehicle's fuel
economy. This setting also cools the air the fastest. After
the vehicle's interior reaches a comfortable temperature,
turn the temperature knob clockwise, to place the air
conditioning system in the normal mode.
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.
If you use the engine coolant heater before starting your
engine in cold weather, 20
F (
-8
C) or lower, your
heating system will produce warmer air faster, to heat
the passenger compartment in cold weather.
The use of an engine coolant heater also 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. For more information, see ªEngine
Coolant Heaterº in the Index.

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3-5 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.
Your vehicle has air outlets in the center and on the sides
of your instrument panel. You can move the outlets from
side
-to-side or up and down to direct the flow of air, or
close the outlets altogether. When you close an outlet, it
will increase the flow of air coming out of any outlets
that are open. These outlets do not completely shut off
airflow when in the closed position.

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3-6
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 to HI 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.
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
toward HI.
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
next to the fan control knob.
The rear window defogger
will only work if the
ignition switch is turned
to RUN. For best results,
clear the window of as
much snow or ice as
possible first.
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.
Do not attach a temporary vehicle license, tape or decals
across the defogger grid on the rear window.