)(Bi-Level):This mode directs half of the air to the
instrument panel vents, then directs the remaining
air to the floor vents. Cooler air is directed to the upper
vents and warmer air to the floor vents.
6(Floor):This mode directs most of the air to the
floor vents. Use this mode to send air to the rear of the
vehicle. Keep the area under the front seats free of
objects that could obstruct airflow to the rear of
the vehicle.
The mode knob can also be used to select the defrost
mode. For more information, see “Defogging and
Defrosting” later in this section.
9(Fan):Turn the left knob clockwise or
counterclockwise to increase or decrease the fan speed.
To increase airflow, turn the knob clockwise. To
decrease airflow, turn it counterclockwise. To turn the
fan off, turn the mode knob on the far right
counterclockwise to the off position.
Temperature Knob:Turn the middle knob located
clockwise or counterclockwise to increase or decrease
the temperature inside of your vehicle. Turn the
knob toward the red area for warmer air. Turn the knob
toward the blue area for cooler air.If your vehicle has air conditioning, the controls will look
like this:
On hot days, open the windows to let hot inside air
escape; then close them. This helps to reduce the time
it takes for your vehicle to cool down. It also helps
the system to operate more efficiently.
<(Maximum Air Conditioning):Turn the right knob
to this setting for maximum cooling. This setting puts
the system in 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.
Y(Air Conditioning):This setting is used for
normal cooling on hot days. It cools outside air and
directs it through the instrument panel vents.
)(Bi-Level Air Conditioning):This setting divides
airflow between the floor vents and instrument panel
vents. The air conditioning compressor will cycle
continuously in this setting as long as the outside
temperature is warm enough to activate the compressor.Vehicles With Air Conditioning
3-21
Defogging and Defrosting
Fog on the inside of windows is a result of high humidity
(moisture) condensing on the cool window glass. This
can be minimized if the climate control is used properly.
There are two modes to clear fog or frost from your
windshield and side windows.
Use the defog mode to clear the windows of fog or
moisture and warm the passengers. Use the defrost
mode to remove fog or frost from the windshield more
quickly. For best results, clear all snow and ice from the
windshield before defrosting.
Turn the mode knob on the right of the climate control
panel to select the defog or defrost mode.
-(Defog):With this setting, the outside air comes out
of both the floor and defroster outlets. Adjust the
temperature knob for warmer or cooler air. The air
conditioning compressor may operate in this setting to
dehumidify the air.
0(Defrost):This setting operates the defroster. Most
of the air comes out near the windshield, with some
going to the floor outlets and front side windows. The air
conditioning compressor may operate in this setting to
dehumidify the air.The defog setting is useful for cold weather with a large
number of passengers or very humid conditions to
help keep the windshield clear. Use defrost to remove
fog or ice from the windshield quickly in extremely
cold conditions. The temperature knob should be in the
red area and the fan control toward high. Do not
drive the vehicle until all the windows are clear.
Rear Window Defogger
The rear window defogger uses a warming grid to
remove fog or frost from the rear window.
Be sure to clear as much snow from the rear window as
possible.
Press this button which is
located near the fan
control to turn the rear
window defogger on or off.
An indicator light in the
button will come on when
the rear window defogger
is working.
The rear window defogger will only work when the
ignition is in RUN.
3-22
Air Brake Systems
If your vehicle has air brakes, it is important to get rid of
moisture in your system. Moisture will damage your
system if it is not removed daily.
There are two ways to do this. One is automatic through
the air brake vehicle’s air dryer with intregal automatic
moisture ejector that purges air from the system through
a self-contained reservoir. The other way to drain
moisture from the air brake system is to manually
activate drain valves at each reservoir. Drain the air
reservoirs occasionally to be sure the air dryer is
working properly.
Drain the air brakes at full system pressure. To be sure
you are at full pressure, check your air pressure
gage. It should read at least 100 psi (692 kPa).
Air Dryer
If your vehicle has air brakes, it will have an air dryer.
This collects and removes dirt, moisture, or other foreign
matter from the air prior to entering the brake system.
The dryer also acts as a moisture ejector. It
automatically ejects the moisture when the compressor
cycles. The purge tank has a manual drain valve
that must be drained every day. See “Air Brake
Systems” for the manual drain procedure. The air dryer
is mounted on the passenger side frame rail.
The dryer has a filter that you need to change at
intervals. SeeScheduled Maintenance on page 6-5for
more about servicing this filter.
5-50
Electric Air Compressor
Your vehicle may have an electric air compressor. This
compressor is used to run options that require
pressurized air, such as air horn, air seat, 7.8L engine
exhaust restrictor, or 7.8L engine exhaust brake.
The air compressor is used when vehicles are not
equipped with an air brake system.
The air supply for this
system must be
maintained by releasing
the drain valve to eject any
moisture that may have
built up in the system.
It is recommended that this system be drained on a
weekly basis.
Clutch Pedal Free Travel
If you have a V8 engine and a manual transmission,
your clutch will need adjustment when pedal free travel
gets down to about 1/4 inch (32 mm), as measured
at the clutch pedal pad. You should have 1 1/2 to
2 inches (38 to 51 mm) of clutch pedal free travel.
If your clutch ever needs service, be sure to use only
GM clutch replacement parts.
Chassis Lubrication
Your Maintenance Schedule provides all of the required
chassis lubrication intervals and identifies proper
lubricants to use. Be sure to see your Maintenance
Schedule before performing any chassis lubrication
service. To determine location of chassis lubrication
items, use the following charts.
5-51
Fuse Usage
ENG 2 Engine 2
HTD FUEL Heated Fuel
BLANK Empty
BLANK Empty
BLANK Empty
A/C COMP Air Conditioning Compressor
ABS 1 Anti-Lock Brake System 1
ABS 2 Anti-Lock Brake System 2
ABS 3 Anti-Lock Brake System 3
ENGINE Engine
E/A PUMP Electronic/Automatic Pump
HORN Horn
NOTE 2L18 Fuel, LG4 Powertrain Control
Valve, LG5 Electronic Control
Module
BLANK Empty
STUD A Spare
STUD B SpareRelay Usage
NOTE 1LG4 Powertrain Control Valve,
L18 Fuel Pump, LG5 Heated Fuel
IGN B Ignition
STARTER Starter
HORN Horn
IGN A Ignition
PTO/ECU*Power Take-Off/Engine Control Unit
Diesel 7.8L DURAMAX
®
REVERSE Reverse
NEUTRAL
STARTNeutral Start
5-93