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 housing
mounted within the passenger compartment under
the instrument panel. The HVAC housing includes:

• A/C Evaporator

• Evaporator temperature sensor

• Blower motor

• Recirculation-air door and actuator

• Blower motor resistor or power module (depend-

ing on application)

• Blend-air doors and actuators

• Heater core

• Mode-air doors and actuator

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

HEATING & AIR CONDITIONING

24 - 1

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 the panel out-
lets 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 HVAC housing, it
is further directed through molded plastic ducts to
the various outlets within the vehicle interior. These
outlets and their locations are as follows:

• Defroster Outlet - A dual, centrally mounted

outlet delivers air for defrosting the large windshield.
An integral grid is molded into the center of the
instrument panel top cover to prevent objects from
falling into the duct.

• Demister Outlets - There are two side window

demisters that aid in defogging and defrosting the
front door windows. One demister outlet is located at
each outboard end of the instrument panel top pad,
near the belt line at the A-pillars.

• Instrument Panel Outlets - There are four

panel outlets in the instrument panel, one located
near each outboard end of the instrument panel fac-
ing the rear of the vehicle, and two located near the
top of the instrument panel center bezel.

• Front Floor Outlets - There are two front

floor outlets, one located above each side of the floor
panel center tunnel below the instrument panel.

• Rear Floor Outlets Rear passenger vents are

located in the center floor console and have separate
blower fan control switch.

AUTOMATIC TEMPERATURE CONTROL (ATC) -
DUAL ZONE

The dual zone automatic temperature control

(ATC) heating-A/C system allows completely indepen-
dent side-to-side temperature control of the discharge
air.

The dual zone ATC system includes a dust and

odor filter. The particulate air filter element is the
same size as the A/C evaporator to ensure ample
capacity. A door at the base of the HVAC housing
below the glove box provides easy access to the par-
ticular air filter element.

FRONT A/C-HEATER CONTROL

The ATC A/C-heater control (Fig. 2) is located in

the instrument panel and contains:

• two temperature set controls for completely

independent side-to-side temperature control of the
discharged air. The full range of temperature that
the system can produce in any mode is available on
either side of the vehicle by independently adjusting
the controls.

• a power on/off switch. Allows the heating-A/C

system to be completely turned Off. The display indi-

cates only the outside temperature when the system
is off.

• a display screen to indicate the heating-A/C sys-

tem operational modes and inside and outside tem-
peratures.

• a dual zone control. Allows the selection of either

single (driver) or dual (driver and passenger) temper-
ature control mode.

• a separate front window defogger on/off switch.

Contains an LED that illuminates to indicate when
the front widow defroster is manually selected.

• a rear window defogger on/off switch. Contains

an LED that illuminates to indicate when the EBL
system is On.

• an air conditioning on/off switch. Contains an

LED that illuminates to indicate when the A/C mode
is manually selected.

• an air recirculation on/off switch. Contains an

LED that illuminates to indicate when the Recircula-
tion mode is manually selected.

• a manual mode switch. Allows the operator to

manually select the air delivery mode.

• two infrared temperature sensors which inde-

pendently measure the surface temperature of the
driver and front seat passenger.

• a manual blower fan speed switch. Allows the

operator to manually select six different fan speeds.

• a outside temperature switch. Allows the opera-

tor to select either outside air or passenger set tem-
peratures.

• a rear blower fan switch. Allows the operator to

set the rear blower fan speed to AUTO for automatic
speed adjustment, or to REAR to give control to the
intermediate seat occupants, or OFF to shut the rear
blower motor down.

• an auto high and an auto low switch. Allows

various modes of automatic temperature control oper-
ation. Contains LEDs that illuminate to indicate
when operational.

The Computer logic remembers the settings of the

A/C-heater controls when the ignition is turned to
Off and, retains those settings after a restart, etc.
The computer logic also provides variable air recircu-
lation under high temperature and humidity condi-
tions. Recirculation mode is initially accompanied by
outside air to help remove any humidity within the
passenger compartment and will gradually approach
full recirculation over a broad range of temperatures.

REAR A/C-HEATER CONTROL

Primary controls for the rear compartment is on

the instrument panel. The front A/C-heater control
allows the driver to set the rear compartment blower
fan speed, turn the rear unit off, or to give control to
the intermediate seat occupants by switching to the
REAR position. When the rear system is controlled

24 - 2

HEATING & AIR CONDITIONING

HEATING & AIR CONDITIONING (Continued)

from the instrument panel, rear blower fan speed is
automatically controlled based on the front A/C-
heater control temperature setting. Air flow through
the floor console is directed through upper or lower
outlets based on the front mode settings.

The rear rotary blower fan control is centrally

mounted on the center floor console between the sec-
ond row seats and allows control of the rear blower
fan speed by intermediate seat passengers.

MANUAL TEMPERATURE CONTROL (MTC) -
DUAL ZONE

The dual zone manual temperature control (MTC)

heating-A/C system allows completely independent
side-to-side temperature control of the discharge air.

The MTC A/C-heater control (Fig. 3) is located in

the instrument panel and contains:

• a power on/off switch. Contains an LED that

illuminates to indicate when the heating-A/C system
is On.

• a rear window defogger on/off switch. Contains

an LED that illuminates to indicate when the EBL
system is On.

• slide controls for completely independent side-to-

side temperature control of the discharged air. The
full range of temperature that the heating-A/C sys-
tem 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 on/off switch. Contains an

LED that illuminates to indicate when the heating-
A/C system is in the Recirculation mode.

• an air conditioning on/off switch. Contains an

LED that illuminates to indicate when the heating-
A/C system is in the A/C mode.

• a rotary control to manually select the air deliv-

ery mode.

• a rotary control to manually select the blower

fan speed.

OPERATION

HEATING AND A/C SYSTEMS

Both the dual zone manual temperature control

(MTC) and the dual zone automatic temperature con-
trol (ATC) heating-A/C systems are blend-air type
systems. In a blend-air heating-A/C system (Fig. 4), a
blend-air door controls the amount of conditioned air
that is allowed to flow through, or around, the heater
core. In the dual zone systems used on this model,
two blend-air doors are used to provide completely
independent side-to-side temperature control of the

Fig. 2 ATC Dual Zone Front A/C-Heater Control

1 - A/C-HEATER CONTROL (ATC DUAL ZONE)
2 - INDEPENDENT TEMPERATURE CONTROLS
3 - POWER SWITCH
4 - DISPLAY SCREEN
5 - ZONE MODE CONTROL
6 - MANUAL FRONT WINDOW DEFROSTER SWITCH
7 - REAR WINDOW DEFROSTER (EBL) SWITCH
8 - MANUAL A/C MODE SWITCH
9 - MANUAL RECIRCULATION MODE SWITCH
10 - MANUAL AIR DELIVERY MODE SWITCH
11 - INFRARED TEMPERATURE SENSORS
12 - MANUAL BLOWER FAN SPEED SWITCH
13 - OUTSIDE TEMPERATURE SWITCH
14 - REAR BLOWER FAN SPEED SWITCH
15 - AUTO HIGH/LOW CONTROL SWITCHES

Fig. 3 MTC Dual Zone A/C-Heater Control

1 - A/C-HEATER CONTROL
2 - POWER SWITCH
3 - REAR WINDOW DEFOGGER (EBL) SWITCH
4 - TEMPERATURE CONTROLS
5 - RECIRCULATION MODE SWITCH
6 - A/C MODE SWITCH
7 - AIR DELIVERY CONTROL
8 - BLOWER FAN SPEED CONTROL

HEATING & AIR CONDITIONING

24 - 3

HEATING & AIR CONDITIONING (Continued)

discharge air. The temperature controls determines
the discharge air temperatures by operating the two
blend door actuators, which move the blend-air doors.
This design allows almost immediate control of out-
put air temperatures.

The heating-A/C systems pulls outside (ambient)

air through the cowl opening at the base of the wind-
shield, then into the air inlet housing above the heat-
ing, ventilation and air conditioning (HVAC) housing.
From the air inlet housing the air passes through the
A/C evaporator and then can be directed either
through or around the heater core. This is done by
adjusting the blend-air doors with the temperature
controls located on the front A/C-heater control in the
instrument panel. The air flow can then be directed
from the panel, floor and defrost outlets in various
combinations using the mode control located on the
A/C-heater control. Air flow velocity can be adjusted
with the blower fan speed control located on the A/C-
heater control.

On all models, the outside air intake can be shut

off by selecting the Recirculation Mode. This will
operate a electrically actuated recirculation-air door
that closes off the fresh air intake and recirculates
the air that is already inside the vehicle.

The A/C compressor can be engaged in any mode

by pressing the snowflake, A/C on/off button. It can
also be engaged by placing the mode control 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 on the A/C-
heater control is used to also direct the conditioned
air to the selected system outlets. The mode control
uses an electric actuator to control the mode-air
doors.

The defroster outlet receives airflow from the

HVAC housing through the molded plastic defroster
duct, which connects to the HVAC housing defroster

outlet. The airflow from the defroster outlets is
directed by fixed vanes in the defroster outlet grille
and cannot be adjusted.

The side window demister outlets receive airflow

from the HVAC housing through the molded plastic
defroster duct and molded plastic demister ducts.
The airflow from the side window demister outlets is
directed by fixed vanes in the demister outlet grilles
and cannot be adjusted. The demisters direct air
from the HVAC housing through the outlets located
on the top corners of the instrument panel. The
demisters operate when the mode control knob is
positioned in the floor-defrost and defrost-only set-
tings. Some air may be noticeable from the demister
outlets when the mode control is in the bi-level to
floor positions or when in automatic mode (depending
on application).

The panel outlets receive airflow from the HVAC

housing through a molded plastic main panel duct,
center panel duct and two end panel ducts. The two
end panel ducts direct airflow to the left and right
instrument panel outlets, while the center panel duct
directs airflow to the two center bezel outlets. Each
of these outlets can be individually adjusted to direct
the flow of air.

The floor outlets receive airflow from the HVAC

housing through the floor distribution duct. The front
floor outlets are integral to the molded plastic floor
distribution duct, which is secured to the bottom of
the housing. The front floor outlets cannot be
adjusted. When equipped, the rear console outlets
receive air flow through a duct which is integral to
the floor console. The floor console outlets can be
individually adjusted to direct the flow of air.

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 A/C system on models so equipped is designed

for the use of non-CFC, R-134a refrigerant and uses
an A/C expansion valve to meter the flow of refriger-
ant to the A/C evaporator. The A/C evaporator cools
and dehumidifies the incoming air prior to blending
it with the heated air. To maintain minimum evapo-

Fig. 4 Typical Blend-Air HVAC System

1 - HEATER CORE
2 - BLEND-AIR DOOR (2 DOORS IN DUAL ZONE)
3 - A/C EVAPORATOR
4 - RECIRCULATION-AIR DOOR
5 - FLOOR MODE-AIR DOOR
6 - PANEL/DEFROST MODE-AIR DOOR

24 - 4

HEATING & AIR CONDITIONING

HEATING & AIR CONDITIONING (Continued)

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