Dodge ZB 2005 Service Manual page 1031

24 - 2 HEATING & AIR CONDITIONING
HEATING & AIR CONDITIONING (Continued)
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.
OPERATION
The manual temperature control (MTC) heating-
A/C system is a blend-air type system (Fig. 2). 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. The temperature
control determines the discharge air temperature by
operating the blend door actuator, which move the
blend-air door. This design allows almost immediate
control of output air temperature.
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 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 HVAC 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 created within the 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
intake-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 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. When A/C is selected, the
A/C compressor is cycled on and off as needed by the
A/C-heater control, powertrain control module (PCM)
and the A/C low pressure switch. 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 motor to control the
mode doors.
The A/C system is designed for the use of non-CFC,
R-134a refrigerant and uses an A/C variable orifice
tube to meter the flow of refrigerant to the A/C evap-
orator. The A/C evaporator cools and dehumidifies
the incoming air prior to blending it with the heated
air.
Fig. 2 Typical 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
DIAGNOSIS AND TESTING
A/C PERFORMANCE
The A/C system is designed to provide the passen-
ger compartment with low temperature and low
humidity air. The A/C evaporator, located in the
HVAC housing is cooled to temperatures near the
freezing point. As warm damp air passes over the
fins of the A/C evaporator, the air transfers its heat
to the refrigerant in the evaporator coils and the
moisture in the air condenses on the evaporator fins.
During periods of high heat and humidity, an A/C
system will be more effective in the Recirculation
mode (max-A/C). With the system in the Recircula-
tion mode, only air from the passenger compartment
passes through the A/C evaporator. As the passenger
compartment air dehumidifies, the A/C system per-
formance levels rise.
Humidity has an important bearing on the temper-
ature of the air delivered to the interior of the vehi-
cle. It is important to understand the effect that
humidity has on the performance of the A/C system.
When humidity is high, the A/C evaporator has to
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