obstructions for the heater-A/C 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 ple-
num screen can accumulate within the heater-A/C
housing. The closed, warm, damp and dark environ-
ment created within the heater-A/C 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 dis-
charged into the passenger compartment during
heater-A/C system operation.
Both the manual and AZC heater and air condi-
tioner are blend-air type systems. In a blend-air sys-
tem,
a
blend-air
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 heater-A/C
control panel determines the discharge air tempera-
ture by energizing the blend-air door motor, which
operates the blend-air door. This allows an almost
immediate control of the output air temperature of
the system. The AZC system will have separate
blend-air doors and temperature controls for each
front seat occupant.
The mode control knob on the heater-A/C control
panel is used to direct the conditioned air to the
selected system outlets. On manual temperature con-
trol systems, the mode control knob switches engine
vacuum to control the mode doors, which are oper-
ated by vacuum actuator motors. On AZC systems,
the mode control knob switches electrical current to
control the mode doors, which are operated by elec-
tronic actuator motors.
The outside air intake can be shut off on manual
temperature control systems by selecting the Recircu-
lation 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 recirculating air
door that closes off the outside fresh air intake and
recirculates the air that is already inside the vehicle.
The air conditioner for all models is designed for
the use of non-CFC, R-134a refrigerant. The air con-
ditioning system has an evaporator to cool and dehu-
midify the incoming air prior to blending it with the
heated air. This air conditioning system uses a vari-
able orifice tube in the liquid line near the condenser
outlet tube to meter refrigerant flow to the evapora-
tor coil. To maintain minimum evaporator tempera-
ture
and
prevent
evaporator
freezing,
a
fixed
pressure setting switch on the accumulator cycles the
compressor clutch.
HEATER AND AIR CONDITIONER CONTROL
DESCRIPTION
The manual temperature control heater-A/C sys-
tem uses a combination of electrical, and vacuum
controls. The Automatic Zone Control (AZC) heater-
A/C system uses only electrical controls. These con-
trols provide the vehicle operator with a number of
setting options to help control the climate and com-
fort within the vehicle. Refer to the owner’s manual
in the vehicle glove box for more information on the
suggested operation and use of these controls.
Both heater-A/C control panels are located on the
instrument panel inboard of the steering column and
below the radio (Fig. 5). Both control panels contain
rotary-type temperature control knob(s), a rotary-
type mode control switch knob, a rotary-type blower
motor speed switch knob and an air conditioning
compressor push button switch. The Rear Window
Defogger push button switch is also located on heat-
er–A/C control panel. The AZC control panel also fea-
tures a Recirc push button switch and a vacuum
fluorescent display area.
OPERATION
The AZC control module uses infrared sensing
technology to control occupant comfort levels, not the
actual passenger compartment air temperature. Dual
infrared sensors mounted in the face of the control
Fig. 4 Common Blend-Air Heater-Air Conditioner
System
1 – TEMPERATURE BLEND/AIR DOOR
2 – EVAPORATOR CORE
3 – BLOWER
4 – PANEL DEFROST DOOR
5 – HEAT DEFROST DOOR
6 – HEATER CORE
7 – RECIRCULATING AIR DOOR
24 - 6
HEATING AND AIR CONDITIONING
WJ
DESCRIPTION AND OPERATION (Continued)