conditioning system, manually controlled dual zone
type heating-air conditioning system, manually con-
trolled three zone type heating-air conditioning sys-
tem or an automatic controlled three zone type
heating-air conditioning system is available on this
model.

To maintain the performance level of the heating,

ventilation and air conditioning (HVAC) system, the
engine cooling system must be properly maintained.
The use of a bug screen is not recommended. Any
obstructions in front of the radiator or A/C condenser
will reduce the performance of the A/C and engine
cooling systems.

The engine cooling system includes the radiator,

thermostat, radiator hoses and the engine coolant
pump. Refer to 7 - Cooling for more information
before opening or attempting any service to the
engine cooling system.

All vehicles are equipped with a common heater,

ventilation and air conditioning (HVAC) housing (Fig.
1). The system combines air conditioning, heating,
and ventilating capabilities in a single unit housing
mounted within the passenger compartment under
the instrument panel. The HVAC housing includes:

• Blower motor

• Blower motor resistor or power module (depend-

ing on application)

• Heater core

• A/C evaporator

• Blend-air doors and actuator(s)

• Mode-air doors and actuator

• Recirculation-air door and actuator
Based upon the system and mode selected, condi-

tioned air can exit the HVAC housing through one or
a combination of the three main housing outlets:
defrost, panel or floor. The defrost and panel outlets
are located on the top of the housing and the floor
outlet is located on the bottom of the housing. Once
the conditioned air exits the unit housing, it is fur-
ther directed through molded plastic ducts to the var-
ious outlets in the vehicle interior. These outlets and
their locations are as follows:

• Defroster Outlet - A single large defroster out-

let is located in the center of the instrument panel
top cover, near the base of the windshield.

• Side Window Demister Outlets - There are

two side window demister outlets, one is located at
each outboard end of the instrument panel, near the
A-pillars.

• Panel Outlets - There are five panel outlets in

the instrument panel, one located near each outboard
end of the instrument panel facing the rear of the
vehicle and three located near the top of the instru-
ment panel center bezel.

• Front Floor Outlets - There are two front floor

outlets, one located above each side of the center of
the floor panel near the dash panel.

HEATING & AIR CONDITIONING

24 - 1

MANUAL SINGLE ZONE

The manual single zone heating and A/C system

allows one temperature setting for the entire vehicle.
The full range of temperatures that the system can
produce are available by rotating the temperature
control located on the A/C-heater control.

The A/C-heater control and integral computer is

located in the instrument panel and contains:

• a rear window defogger on/off switch. Contains

an LED that illuminates to show when the function
is operational.

• an air recirculation on/off switch. The Recircu-

late button contains an LED that illuminates to show
when the function is in operation.

• an air conditioning on/off switch. The Snowflake

button contains an LED that illuminates to shown
when the function is in operation.

• a rotary knob for fan speed selection and turn-

ing the heater-A/C system off.

• a rotary knob for temperature control of the dis-

charged air.

• a rotary knob for mode control.

MANUAL DUAL ZONE

The manual dual zone heating and A/C system

allows completely independent side-to-side tempera-
ture control of the discharge air.

The A/C-heater control and integral computer is

located in the instrument panel and contains:

• a rear window defogger on/off switch. Contains

an LED that illuminates to show when the function
is operational.

• slide controls for completely independent side-to-

side temperature control of the discharged air. The
full range of temperature that the system can pro-
duce in any mode is available on either side of the
vehicle by independently positioning the slide con-
trols on the instrument panel.

• an air recirculation on/off switch. The Recircu-

late button contains an LED that illuminates to show
when the function is in operation.

• an air conditioning on/off switch. The Snowflake

button contains an LED that illuminates to shown
when the function is in operation.

• a rotary knob for fan speed selection and turn-

ing the heater-A/C system off.

• a rotary knob for mode control.

MANUAL THREE ZONE

The fully adjustable manual three zone front and

rear heating and A/C system allows intermediate
seat passengers the ability to regulate air tempera-
ture as well as fan speed and provides floor outlets to
the rear of the right sliding door and overhead out-
lets at each rear outboard seating position. Primary
control for the rear blower is on the front A/C-heater
control. All controls are identified by ISO graphic
symbols.

FRONT CONTROL PANEL

The front A/C-heater control and integral computer

mounted in the instrument panel contains:

• a rear window defogger on/off switch.

• slide controls for completely independent side-to-

side temperature control of the discharge air. The full
range of temperature that the system can produce in
any mode is available on either side of the vehicle by
independently positioning the slide controls on the
instrument panel.

• an air recirculation button. The Recirculate but-

ton contains an LED that illuminates to show when
the function is in operation.

• an air conditioning button that allows the com-

pressor to be turned on/off. The Snowflake button
contains an LED that illuminates to shown when the
function is in operation.

• a rotary knob for front fan speed selection and

turning the heater-A/C system off.

• a rotary knob for rear fan speed selection.

• a rotary knob for mode control.

Fig. 1 HVAC Housing

1 - HVAC HOUSING
2 - A/C EVAPORATOR
3 - EVAPORATOR TEMPERATURE SENSOR
4 - BLOWER MOTOR
5 - RECIRCULATION DOOR ACTUATOR
6 - BLOWER POWER MODULE/RESISTOR BLOCK
7 - BLEND DOOR ACTUATORS
8 - HEATER CORE
9 - MODE DOOR ACTUATOR

24 - 2

HEATING & AIR CONDITIONING

HEATING & AIR CONDITIONING (Continued)

REAR CONTROL PANEL

The rear A/C-heater control centrally mounted in

the headliner allows intermediate seat passengers to
adjust rear air distribution, temperature and blower
motor speed when the center knob on the front A/C-
heater control is set to the Rear position. The rear
A/C-heater control contains:

• a rotary adjustment knob for temperature.

• a rotary adjustment for fan speed control.

AUTOMATIC TEMPERATURE CONTROL (ATC)

Two different automatic temperature control (ATC)

heating-A/C systems are available for this model
depending on the market.

The Dual-Zone ATC system allows the driver and

front occupants to each select individual comfort tem-
peratures.

The Three-Zone ATC system allows both the driver

and front occupants and the rear intermediate occu-
pants to select individual comfort temperatures.

NOTE: Individual comfort temperatures are the per-
ceived temperature level at the individual seating
areas, NOT the actual passenger compartment air
temperature.

The ATC system includes a particulate air filter.

The filter element is the same size as the A/C evap-
orator to ensure ample capacity. A door at the base of
the HVAC housing below the glove box provides easy
access to the filter element.

The ATC computer utilizes integrated circuitry and

information carried on the programmable communi-
cations interface (PCI) data bus network to monitor
many sensors and switch inputs throughout the vehi-
cle. In response to those inputs, the internal circuitry
and programming of the ATC computer allow it to
control electronic functions and features of the ATC
system. The inputs to the ATC computer are:

• Vehicle Speed/Engine RPM – The ATC com-

puter monitors engine rpm, vehicle speed and mani-
fold

absolute

pressure

information

from

the

powertrain control module (PCM).

• Coolant Temperature – ATC computer moni-

tors coolant temperature received from the PCM and
converts it to degrees Fahrenheit.

• Ambient Temperature – ATC computer moni-

tors ambient temperature from the compass mini trip
computer (CMTC) and converts it to degrees Fahren-
heit.

• Engine Miscellaneous Sensor Status – ATC

computer monitors A/C disable information from the
PCM.

• Refrigerant Pressure – ATC computer moni-

tors barometric pressure, intake air temperature,

high side pressure and methanol content as broad-
cast by the PCM.

• Door Ajar Status – The ATC computer moni-

tors driver front door, passenger front door, left rear
door, right rear door and liftgate ajar information, as
identified by the body control module (BCM), to
determine if all in-car temperatures should be main-
tained.

• Dimming – The ATC computer monitors dim-

ming status from the BCM to determine the required
level of brightness and will dim accordingly.

• Vehicle Odometer – The ATC computer moni-

tors the vehicle odometer information from the BCM
to prevent flashing the vacuum-flourescent (VF) dig-
ital display icons if the manual motor calibration or
manual cool down tests have failed. Flashing of the
display icons will cease when the vehicle odometer is
greater than 3 miles.

• English/Metric – The ATC computer monitors

the English/Metric information broadcast by the
CMTC. The set temp displays for both the front and
rear control heads will be set accordingly.

• Vehicle Identification Number – The ATC

computer monitors the last eight characters of the
VIN broadcast by the PCM and compares it to the
information stored in EEPROM. If it is different, the
new number will be stored over the old one and a
motor calibration shall be initiated.

• A/C System Information – The ATC computer

will send a message for evaporator temperature too
low, fan blower relay status, evaporator sensor fail-
ure, rear window defogger relay and A/C select.

FRONT CONTROL PANEL

The front A/C-heater control and integral computer

is mounted in the instrument panel and contains:

• a power button which allows the system to be

completely turned off. The display is blank when the
system is off.

• a rocker switch that selects a cool-down rate.

LO-AUTO or HI-AUTO are displayed when the sys-
tem is in automatic operation.

• three rocker switches that select comfort temper-

atures from 15° to 30° C (59° to 85° F), which are
shown in the VF digital display. If the set temp is 15°
C (59° F) and the down button is pressed, the set
temp value will become 13° C (55° F) but the display
will show LO. If the set temp is 29° C (85° F) and the
up button is pressed, the set temp value will become
32° C (90° F) but the display will show HIGH. Tem-
peratures can be displayed in either metric or Fahr-
enheit, which is controlled from the overhead console.

• an air conditioning button that allows the com-

pressor to be turned off. A Snowflake symbol is illu-
minated when air conditioning is on, whether under
manual or automatic control.

HEATING & AIR CONDITIONING

24 - 3

HEATING & AIR CONDITIONING (Continued)

• an air recirculation button. A Recirculation sym-

bol appears in the display when the button is
pressed, or when the system exceeds 80 percent recir-
culated air under automatic control due to high air
conditioning demand.

• a rear window defogger on/off switch. A graphic

symbol shows when the defroster is on.

• a rotary knob for front fan speed selection can

override the automatic controls. LEDs surrounding
the knob show the current setting.

• a rotary knob for control of the rear system

(Three-Zone ATC system only).

• a rotary knob for mode control can override the

automatic controls. LEDs surrounding the knob show
the current setting.

• computer logic which remembers the settings of

the controls when the ignition is turned off and
retains those settings after a restart. If the system is
off when the ignition is turned off it will be off when
the engine is restarted, etc.

• computer logic which provides variable air recir-

culation under high temperature and humidity condi-
tions. Because recirculation is generally accompanied
by increased fan noise, the proportion of recirculated
to outside air gradually approaches full recirculation
over a broad temperature range.

• computer logic which enables additional heat for

diesel equipped vehicles by using a supplemental
engine coolant heater.

REAR CONTROL PANEL

The Three-Zone ATC sytem utilizes a rear control

panel centrally mounted on the headliner which
includes a VF digital display, a rocker control for
temperature and rotary controls for adjustment of
mode and fan speed of the rear heating-A/C system
by intermediate seat passengers.

OPERATION

HEATER AND AIR CONDITIONER

The heating and air conditioning systems pulls

outside (ambient) air through the cowl opening at the
base of the windshield and into the plenum chamber
above the heating, ventilation and air conditioning
(HVAC) housing, then through the evaporator coil.
Air flow can be directed either through or around the
heater core by adjusting the blend door with the tem-
perature control knob on the A/C-heater control
located on instrument panel. The air flow can then
be directed out from the panel, floor and defrost out-
lets in various combinations using the mode control
knob located on the A/C-heater control. Air flow
velocity can be adjusted with the blower speed selec-
tor located on the A/C-heater control.

NOTE: It is important to keep the air intake opening
clear of debris. Leaf particles and other debris that
is small enough to pass through the cowl opening
screen can accumulate within the HVAC housing.
The closed, warm, damp and dark environment cre-
ated within the housing is ideal for the growth of
certain molds, mildews and other fungi. Any accu-
mulation of decaying plant matter provides an addi-
tional food source for fungal spores, which enter
the housing with the fresh intake-air. Excess debris,
as well as objectionable odors created by decaying
plant matter and growing fungi can be discharged
into the passenger compartment during heater-A/C
operation if the air intake opening is not kept clear
of debris.

The heater and air conditioning system is a blend-

air type system. In a blend-air system, a blend door
controls the amount of conditioned air that is allowed
to flow through, or around, the heater core. The tem-
perature control knob determines the discharge air
temperature by actuating an electric motor, which
operates the blend door. This allows an almost imme-
diate control of the output air temperature of the sys-
tem.

On all models, the outside air intake can be shut

off by pressing the Recirculation button on the A/C-
heater control. This will operate a electric actuated
recirculation air door that closes off the outside fresh
air intake and recirculates the air that is already
inside the vehicle.

The air conditioning compressor can be engaged in

any mode by pressing the snowflake, A/C on/off but-
ton. It can also be engaged by placing the mode con-
trol in the mix to defrost positions. This will remove
heat and humidity from the air before it is directed
through or around the heater core. The mode control
knob on the A/C-heater control is used to also direct
the conditioned air to the selected system outlets.
The mode control switch uses an electric motor to
control the mode doors.

MANUAL SINGLE ZONE

• The temperature control knob enables continu-

ously variable proportioning of the conditioned air.

• The mode control knob enables continuously

variable proportioning of air flow between modes and
has detents adjacent to each icon.

• The blower control provides four separate speeds

and an Off position.

• When the heater-A/C system is off, the HVAC

computer closes the recirculation door to prevent out-
side air from entering the passenger compartment.

• Interior air may be recirculated to speed up

heating or cooling in all modes except defrost and

24 - 4

HEATING & AIR CONDITIONING

HEATING & AIR CONDITIONING (Continued)

Content .. 1207 1208 1209 1210 ..