24 - 2 HEATING & AIR CONDITIONING

HEATING & AIR CONDITIONING (Continued)

OPERATION - HEATER AND AIR CONDITIONER

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 sys
tem blower housing. Air flow velocity can then be adjusted with the blower
motor 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 created within 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 growing fungi can
be discharged into the passenger compartment during HVAC sys tem operation.

Both the manual and AZC heater and air conditioner are blend-air type
systems. In a blend-air sys tem, a blend door controls the amount of
unconditioned air (or cooled air from the evaporator) that is allowed to
flow through, or around, the heater core. A temperature control knob on the
a/c heater control panel determines 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 sys
tem. The AZC system will have separate blend doors and temperature controls
for each front seat occupant.

The mode control knob on the a/c heater control panel is used to direct the
conditioned air to the selected system outlets. On manual temperature
control systems, the mode control knob switches engine vacuum to control the
mode doors, which are operated by vacuum actuators. On AZC systems, the mode
control knob switches electrical current to control the mode doors, which
are operated by electronic actuators.

The outside air intake can be shut off on manual temperature control systems
by selecting the Recirculation Mode with the mode control knob. The outside

Air intake can be shut off on Automatic Zone Control (AZC) type system by
pushing the Recirculation Mode button. This will operate the recirculation
door that closes off the outside fresh air Intake and recalculates the air
that is already inside the vehicle.

The air conditioner for all models is designed for the use of non-CFC, R- I
34a 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 evaporator temperature and
prevent evaporator freezing, the system utilizes an evaporator thermister
probe with the appropriate operating logic located in the body control
module (BCM).

OPERATION - REFRIGERANT SYSTEM SERVICE PORT

The high pressure service port is located on the liquid line near the
receiver/drier. The low pressure ser vice port is located on the suction
line near the evaporator at the rear of the engine compartment.

Each of the service ports has a threaded plastic protective cap installed
over it from the factory after servicing the refrigerant system; always
reinstall both of the service port caps.

DIAGNOSIS AND TESTING - A/C PERFORMANCE

The air conditioning system is designed to provide the passenger compartment
with low temperature and low specific humidity air. The evaporator, located
in the HVAC housing on the dash panel below the instrument panel, is cooled
to temperatures near the freezing point. As warm damp air passes through the
cooled evaporator, the air transfers its heat to the refrigerant in the
evaporator and the moisture in the air condenses on the evaporator fins.
During periods of high heat and humidity, an air conditioning sys tem will
be more effective in the Recirculation Mode. With the system in the
Recirculation Mode, only air from the passenger compartment passes through
the evaporator. As the passenger compartment air dehumidifies, the air
conditioning system performance levels improve.