To maintain the performance level of the heating-air conditioning system, the engine cooling system must be prop-
erly maintained. Any obstructions in front of the radiator or condenser will reduce the performance of the air con-
ditioning and engine cooling systems.

The heating system includes the radiator, heater core and the heater hoses. Refer to Cooling for more information
before opening, or attempting any service to the engine cooling system.

A manual dual-zone temperature control type heating-air conditioning system is factory-installed on this model.

This vehicle is equipped with a common HVAC housing assembly. The system combines air conditioning, heating,
and ventilating capabilities in a single unit housing mounted under the instrument panel.

OPERATION

Outside fresh air enters the vehicle through the cowl top opening at the base of the windshield, and passes through
a plenum chamber to the HVAC system blower housing. Air flow velocity can then be adjusted with the blower motor

HEATING & AIR CONDITIONING

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speed selector switch on the A/C heater control panel. The air intake openings must be kept free of snow, ice,
leaves, and other obstructions for the HVAC system to receive a sufficient volume of outside air.

It is also important to keep the air intake openings clear of debris because leaf particles and other debris that is
small enough to pass through the cowl plenum screen can accumulate within the HVAC housing. The closed, warm,
damp and dark environment in the HVAC housing is ideal for the growth of certain molds, mildews and other fungi.
Any accumulation of decaying plant matter provides an additional food source for fungal spores, which enter the
housing with the fresh air. Excess debris, as well as objectionable odors created by decaying plant matter and grow-
ing fungi can be discharged into the passenger compartment during HVAC system operation.

In a blend-air system, a blend door controls the amount of unconditioned air (or cooled air from the evaporator) that
is allowed to flow through and around, the heater core. A temperature control on the A/C heater control panel deter-
mines the discharge air temperature by energizing the blend door actuator, which operates the blend door. This
allows an almost immediate control of the output air temperature of the system.

The mode control on the A/C heater control panel is used to direct the conditioned air to the selected system out-
lets. The mode control uses engine vacuum to control the mode doors, which are operated by vacuum actuators.

The outside air intake can be shut off on manual temperature control systems by selecting the Recirculation Mode
with the mode control. This will operate the recirculation door that closes off the outside fresh air intake and recir-
culates the air that is already inside the vehicle.

The air conditioner is designed for the use of non-CFC, R-134a refrigerant. The air conditioning system has an
evaporator to cool and dehumidify the incoming air prior to blending it with the heated air. This air conditioning
system uses a thermal expansion valve to meter refrigerant flow to the evaporator coil. To maintain minimum evap-
orator temperature and prevent evaporator freezing, the system utilizes an evaporator thermister probe with the
appropriate operating logic located in the A/C Heater Control Module.

DIAGNOSIS AND TESTING

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HEATING & AIR CONDITIONING - ELECTRICAL DIAGNOSTICS

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