Dodge Durango (DN). Manual — part 187

EVAPORATOR COIL

FRONT

DESCRIPTION

The evaporator coil is located in the heater-A/C

housing, under the instrument panel. The evaporator
coil is positioned in the heater-A/C housing so that
all air that enters the housing must pass over the
fins of the evaporator before it is distributed through
the system ducts and outlets. However, air passing
over the evaporator coil fins will only be conditioned
when the compressor is engaged and circulating
refrigerant through the evaporator coil tubes.

OPERATION

Refrigerant enters the evaporator from the expan-

sion valve as a low-temperature, low-pressure mix-
ture of liquid and gas. As air flows over the fins of
the evaporator, the humidity in the air condenses on
the fins, and the heat from the air is absorbed by the
refrigerant. Heat absorption causes the refrigerant to
boil and vaporize. The refrigerant becomes a low-
pressure gas when it leaves the evaporator.

The evaporator coil cannot be repaired and, if

faulty or damaged, it must be replaced.

REAR

DESCRIPTION

The rear evaporator coil is located in the rear over-

head A/C unit housing, above the headliner. The
evaporator coil is positioned in the overhead A/C unit
housing so that all air that enters the housing must
pass over the fins of the evaporator before it is dis-
tributed through the system outlets. However, air
passing over the evaporator coil fins will only be con-
ditioned when the compressor is engaged and circu-
lating refrigerant through the evaporator coil tubes.

OPERATION

Refrigerant enters the evaporator from the rear

expansion valve as a low-temperature, low-pressure
mixture of liquid and gas. As air flows over the fins
of the evaporator, the humidity in the air condenses
on the fins, and the heat from the air is absorbed by
the refrigerant. Heat absorption causes the refriger-
ant to boil and vaporize. The refrigerant becomes a
low-pressure gas when it leaves the evaporator.

The rear evaporator coil cannot be repaired and, if

faulty or damaged, the rear evaporator coil must be
replaced.

EXPANSION VALVE

FRONT

DESCRIPTION

The front “H” valve-type thermal expansion valve

(TXV) is located at the dash panel between the liquid
and suction lines, and the evaporator coil. High-pres-
sure, high temperature liquid refrigerant from the
liquid line passes through the expansion valve ori-
fice, converting it into a low-pressure, low-tempera-
ture mixture of liquid and gas before it enters the
evaporator coil.

OPERATION

A sensor in the expansion valve control head mon-

itors the temperature and pressure of the refrigerant
leaving the evaporator coil through the suction line,
and adjusts the orifice size at the liquid line to let
the proper amount of refrigerant into the evaporator
coil to meet the vehicle cooling requirements. Con-
trolling the refrigerant flow through the evaporator
ensures that none of the refrigerant leaving the evap-
orator is still in a liquid state, which could damage
the compressor.

The expansion valve is a factory calibrated unit

and cannot be adjusted or repaired. If faulty or dam-
aged, the expansion valve must be replaced.

REAR

DESCRIPTION

Vehicles equipped with the optional rear overhead

A/C unit have an H-type thermal expansion valve
(TXV) located underneath the passenger side of the
vehicle floor panel, next to the sill. It performs the
same function as the front expansion valve, to moni-
tor refrigerant temperature and pressure at the con-
trol head and meter the refrigerant entering the
evaporator to meet the vehicle cooling requirements.

OPERATION

The rear expansion valve is a factory calibrated

unit and cannot be adjusted or repaired. If faulty or
damaged, the rear expansion valve unit must be
replaced.

FILTER-DRIER

DESCRIPTION

The filter-drier is mounted on the right front

wheelhouse front extension in the engine compart-
ment, in the liquid line between the condenser outlet
and the evaporator inlet. Refrigerant enters the fil-
ter-drier as a high-pressure, high-temperature liquid.

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HEATING AND AIR CONDITIONING

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DESCRIPTION AND OPERATION (Continued)

OPERATION

The filter-drier performs a filtering action to pre-

vent foreign material in the refrigerant from contam-
inating the expansion valve. A desiccant bag is
mounted inside the filter-drier canister to absorb any
moisture which may have entered and become
trapped within the refrigerant system. In addition,
during periods of high demand air conditioner opera-
tion, the filter-drier acts as a reservoir to store sur-
plus refrigerant.

The filter-drier cannot be repaired. If the filter-

drier is faulty or damaged, or if the refrigerant sys-
tem has been contaminated or left open to the
atmosphere for an indeterminable period, it must be
replaced.

HEATER AND AIR CONDITIONER

DESCRIPTION

All vehicles are equipped with a common heater-

A/C housing assembly (Fig. 4). The system combines
air conditioning, heating, and ventilating capabilities
in a single unit housing mounted under the instru-
ment 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 heater-A/C
system blower housing. Air flow velocity can then be
adjusted with the blower motor speed selector switch

on the heater-A/C control panel. The air intake open-
ings must be kept free of snow, ice, leaves, and other
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.

The heater and air conditioner are blend-air type

systems. In a blend-air system, a blend-air door con-
trols 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 temperature by moving a cable, which
operates the blend-air door. This allows an almost
immediate manual control of the output air tempera-
ture of the system.

The mode control knob on the heater-A/C control

panel is used to direct the conditioned air to the
selected system outlets. The mode control switch uses
engine vacuum to control the mode doors, which are
operated by vacuum actuator motors.

The outside air intake can be shut off by selecting

the recirculation mode (Max A/C) with the mode con-
trol knob. This will operate a vacuum actuated recir-
culating air door that closes off the outside fresh air
intake and recirculates the air that is already inside
the vehicle.

A large central duct delivers conditioned air from

the front heater-A/C housing to the second and third
seat floor panel foot wells. A damper door in this duct
can be adjusted by the second seat passengers with a
manual control located on a mini-console just behind
the split bench seat center cushion, or located on the
upper rear surface of the floor console on models with
the optional bucket seats. The split bench seat con-
trol has two positions: On or Off. The bucket seat
control has three positions: On, Off and a third posi-
tion that directs air flow through a pair of adjustable
barrel outlets mounted high on the rear surface of
the floor console.

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

Fig. 4 Common Blend-Air Heater-Air Conditioner

System - Typical

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

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HEATING AND AIR CONDITIONING

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DESCRIPTION AND OPERATION (Continued)

heated air. This air conditioning system uses a ther-
mal expansion valve between the condenser and the
evaporator coil to meter refrigerant flow to the evap-
orator coil. To maintain minimum evaporator temper-
ature and prevent evaporator freezing, an electronic
cycling clutch switch on the expansion valve cycles
the compressor clutch.

HEATER AND AIR CONDITIONER CONTROL

DESCRIPTION

The heater and A/C system use a combination of

mechanical, electrical, and vacuum controls. These
controls provide the vehicle operator with a number
of setting options to help control the climate and
comfort within the vehicle. Refer to the owner’s man-
ual in the vehicle glove box for more information on
the features, use, and suggested operation of these
controls.

OPERATION

The heater-A/C control panel is located to the right

of the instrument cluster on the instrument panel.
The control panel contains a rotary-type temperature
control knob, a rotary-type mode control switch knob,
and a rotary-type blower motor speed switch knob.

The heater-A/C control panel cannot be repaired. If

faulty or damaged, the entire unit must be replaced.
The illumination lamps are available for service
replacement.

HEATER CORE

DESCRIPTION

The heater core is located in the heater-A/C hous-

ing, under the instrument panel. It is a heat
exchanger made of rows of tubes and fins.

OPERATION

Engine coolant is circulated through heater hoses

to the heater core at all times. As the coolant flows
through the heater core, heat removed from the
engine is transferred to the heater core fins and
tubes. Air directed through the heater core picks up
the heat from the heater core fins. The blend air door
allows control of the heater output air temperature
by controlling how much of the air flowing through
the heater-A/C housing is directed through the
heater core. The blower motor speed controls the vol-
ume of air flowing through the heater-A/C housing.

The heater core cannot be repaired and, if faulty or

damaged, it must be replaced. Refer to Cooling Sys-
tem for more information on the engine cooling sys-
tem, the engine coolant and the heater hoses.

HIGH PRESSURE CUT-OFF SWITCH

DESCRIPTION

The high pressure cut-off switch is located on the

discharge line near the compressor. The switch is
screwed onto a fitting that contains a Schrader-type
valve, which allows the switch to be serviced without
discharging the refrigerant system. The discharge
line fitting is equipped with an O-ring to seal the
switch connection.

OPERATION

The high pressure cut-off switch is connected in

series electrically with the electronic cycling clutch
switch, the low pressure cut-off switch, and the Heat-
er-A/C controls between ground and the Powertrain
Control Module (PCM). The switch contacts open and
close causing the PCM to turn the compressor clutch
on and off. This prevents compressor operation when
the discharge line pressure approaches high levels.

The high pressure cut-off switch contacts will open

when the discharge line pressure rises above about
3100 to 3375 kPa (450 to 490 psi). The switch con-
tacts will close when the discharge line pressure
drops to about 1860 to 2275 kPa (270 to 330 psi).

The high pressure cut-off switch is a factory-cali-

brated unit. The switch cannot be adjusted or
repaired and, if faulty or damaged, it must be
replaced.

HIGH PRESSURE RELIEF VALVE

DESCRIPTION

A high pressure relief valve is located on the com-

pressor cylinder head, which is at the rear of the
compressor. This mechanical valve is designed to
vent refrigerant from the system to protect against
damage to the compressor and other system compo-
nents, caused by condenser air flow restriction or an
overcharge of refrigerant.

OPERATION

The high pressure relief valve vents the system

when a discharge pressure of 3445 to 4135 kPa (500
to 600 psi) or above is reached. The valve closes with
a minimum discharge pressure of 2756 kPa (400 psi)
is reached.

The high pressure relief valve vents only enough

refrigerant to reduce the system pressure, and then
re-seats itself. The majority of the refrigerant is con-
served in the system. If the valve vents refrigerant, it
does not mean the valve is faulty.

The high pressure relief valve is a factory-cali-

brated

unit.

The

valve

cannot

be

adjusted

or

repaired, and must not be removed or otherwise dis-

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HEATING AND AIR CONDITIONING

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DESCRIPTION AND OPERATION (Continued)

turbed. The valve is only serviced as a part of the
compressor assembly.

LOW PRESSURE CUT-OFF SWITCH

DESCRIPTION

The low pressure cut-off switch is located on the

suction line jumper tube. The switch is screwed onto
a fitting that contains a Schrader-type valve, which
allows the switch to be serviced without discharging
the refrigerant system. The fitting is equipped with
an O-ring to seal the switch connection.

OPERATION

The low pressure cut-off switch is connected in

series electrically with the high pressure cut-off
switch,

the

heater-A/C

controls,

the

Electronic

Cycling Clutch Switch (ECCS), between ground, and
the Powertrain Control Module (PCM). The switch
contacts open and close causing the PCM to turn the
compressor clutch on and off. This regulates the
refrigerant system pressure, ensuring a sufficient
amount of refrigerant throughout the system.

The low pressure cut-off switch contacts will open

when the suction pressure is about 48 to 90 kPa (7 to
13 psi) or lower. The switch contacts will close when
the suction pressure rises to about 103 to 193 kPa
(15 to 28 psi) or above. Lower ambient temperatures,
below about -1° C (30° F), will also cause the switch
contacts to open. This is due to the pressure/temper-
ature relationship of the refrigerant in the system.

The low pressure cut-off switch is a factory-cali-

brated unit. It cannot be adjusted or repaired and, if
faulty or damaged, it must be replaced.

REAR OVERHEAD AIR CONDITIONER

DESCRIPTION

A rear overhead air conditioning unit is an avail-

able option to supplement the output of the front air
conditioner, for increased rear seat passenger com-
fort. This unit includes a roof-mounted evaporator
coil and a blower motor with a wide squirrel-cage
type blower wheel. A four position (three speeds plus
off) rear blower motor switch is mounted in the head-
liner behind the right front seat position, where it is
accessible to both the driver and the second seat pas-
sengers.

OPERATION

The wide and shallow rear unit is positioned

between the front and second seats to provide ample
headroom for all vehicle occupants. The headliner is
molded to cover the unit and includes an integral air
intake grille toward the front of the unit, and an
opening for a snap-in outlet bezel that includes four

adjustable outlet barrels toward the rear of the unit.
A condensate tray is integral to the lower unit hous-
ing, and water is drained out of the unit through
hoses located behind the trim on each of the B-pil-
lars.

The rear overhead air conditioner will provide cool-

ing only when an air conditioning mode is selected
with the front heater and A/C controls, but the rear
blower will operate independent of the front controls
to circulate the interior air if desired.

REFRIGERANT

DESCRIPTION

The refrigerant used in this air conditioning sys-

tem is a HydroFluoroCarbon (HFC), type R-134a.
Unlike R-12, which is a ChloroFluoroCarbon (CFC),
R-134a refrigerant does not contain ozone-depleting
chlorine. R-134a refrigerant is a non-toxic, non-flam-
mable, clear, and colorless liquefied gas.

Even though R-134a does not contain chlorine, it

must be reclaimed and recycled just like CFC-type
refrigerants. This is because R-134a is a greenhouse
gas and can contribute to global warming.

OPERATION

R-134a refrigerant is not compatible with R-12

refrigerant in an air conditioning system. Even a
small amount of R-12 added to an R-134a refrigerant
system will cause compressor failure, refrigerant oil
sludge or poor air conditioning system performance.
In addition, the PolyAlkylene Glycol (PAG) synthetic
refrigerant oils used in an R-134a refrigerant system
are not compatible with the mineral-based refriger-
ant oils used in an R-12 refrigerant system.

R-134a refrigerant system service ports, service

tool couplers and refrigerant dispensing bottles have
all been designed with unique fittings to ensure that
an R-134a system is not accidentally contaminated
with the wrong refrigerant (R-12). There are also
labels posted in the engine compartment of the vehi-
cle and on the compressor identifying to service tech-
nicians that the air conditioning system is equipped
with R-134a.

REFRIGERANT LINES

DESCRIPTION

The refrigerant lines and hoses are used to carry

the refrigerant between the various air conditioning
system components. A barrier hose design with a
nylon tube, which is sandwiched between rubber lay-
ers, is used for the R-134a air conditioning system on
this vehicle. This nylon tube helps to further contain
the R-134a refrigerant, which has a smaller molecu-
lar structure than R-12 refrigerant. The ends of the

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HEATING AND AIR CONDITIONING

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DESCRIPTION AND OPERATION (Continued)