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 heating-A/C system combines A/C, heating,
and ventilating capabilities in a single HVAC housing
mounted within the passenger compartment behind
the instrument panel. The HVAC housing includes:

• Blower motor

• Blower motor resistor or power module (depend-

ing on application)

• Heater core

• A/C evaporator

• Evaporator temperature sensor

• Blend-air door and actuator

• Mode-air door and actuator

• Recirculation-air door and actuator
Based upon the mode selected, conditioned 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 HVAC housing and the floor outlet is
located on the bottom of the HVAC housing. Once the

conditioned air exits the HVAC housing, it is further
directed through molded plastic ducts to the outlets
within 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 four panel outlets in

the instrument panel, one located near each outboard
end of the instrument panel facing the rear of the
vehicle and two 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.

• Rear Floor Outlets - There are two rear floor

outlets, one located on each side of the floor console
near the rear of each front seat.

Fig. 1 Common Blend-Air HVAC System

1 - HEATER CORE
2 - BLEND DOOR
3 - A/C EVAPORATOR
4 - RECIRCULATION DOOR
5 - FLOOR/PANEL DOOR
6 - FLOOR/DEFROST DOOR

HEATING & AIR CONDITIONING

24 - 1

OPERATION

The heating-A/C system is a blend-air type system.

In a blend-air system, a blend-air door controls the
amount of conditioned air that is allowed to flow
through, or around, the heater core. A temperature
control on the A/C-heater control is used to adjust
the discharge air temperature. The A/C-heater con-
trol sends a request signal to the body control mod-
ule (BCM) to move the electric blend door actuator(s),
which operate the blend-air door(s). This allows an
almost immediate control of the output air tempera-
ture of the system. The A/C system is designed for
the use of non-CFC, R-134a refrigerant and use an
A/C evaporator to cool and dehumidify the incoming
air prior to blending it with the heated air.

The heating-A/C system 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
and through the A/C evaporator. Air flow can be
directed either through or around the heater core.
This is done by adjusting the blend-air door with the
temperature control located on the 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 speed control 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 outside (fresh) air intake can be shut off by

selecting the Recirculation Mode with the mode con-
trol. This will operate an electrically actuated recir-
culation-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 direct the conditioned air to
the selected system outlets. The A/C-heater control
sends a request signal to the BCM to operate the
electric door actuators.

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 outlet is
directed by fixed vanes in the defroster outlet grille
and cannot be adjusted. The defroster outlet grille is
serviceable from the instrument panel.

The side window demister outlets receive airflow

from the HVAC housing through the molded plastic
demister ducts. The demisters direct air from the
HVAC housing through the outlets located on the top
corners of the instrument panel. The demisters oper-
ate when the mode control is positioned in the
bi-level, floor, floor-defrost and defrost settings. The
airflow from the side window demister outlets is
directed by fixed vanes in the demister outlet grilles
and cannot be adjusted. The demister outlet grilles
are only serviced with the instrument panel top
cover.

The instrument 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
panel outlets. Each of these outlets can be individu-
ally 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 HVAC housing. The floor outlets cannot be
adjusted.

This A/C system uses an A/C expansion valve to

meter the flow of refrigerant to the A/C evaporator.
To maintain minimum evaporator temperature and
prevent evaporator freezing, an evaporator tempera-
ture sensor is used to supply evaporator temperature
input to the BCM. The powertrain control module
(PCM) cycles the A/C compressor clutch off and on as
necessary to protect the A/C system from evaporator
freezing and optimize A/C system performance.

DIAGNOSIS AND TESTING

HEATING AND A/C SYSTEM SELF
DIAGNOSTICS

All automatic temperature control (ATC) and man-

ual temperature control (MTC) system diagnostic

24 - 2

HEATING & AIR CONDITIONING

HEATING & AIR CONDITIONING (Continued)

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