Refrigerant System Service Ports; Vacuum Check Valve; Vacuum Reservoir; Diagnosis And Testing A/C Performance - Dodge 2000 DURANGO Service Manual

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DESCRIPTION AND OPERATION (Continued)

REFRIGERANT SYSTEM SERVICE PORTS

DESCRIPTION
The two refrigerant system service ports are used
to charge, recover/recycle, evacuate, and test the air
conditioning refrigerant system. Unique service port
coupler sizes are used on the R-134a system, to
ensure that the refrigerant system is not accidentally
contaminated by the use of the wrong refrigerant
(R-12), or refrigerant system service equipment.
OPERATION
The high pressure service port is located on the liq-
uid line between the condenser and the evaporator,
near the front of the engine compartment. The low
pressure service port is located on the compressor
manifold, directly over the suction port of the com-
pressor.
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.

VACUUM CHECK VALVE

DESCRIPTION
Two vacuum check valves are installed in the
accessory vacuum supply line in the engine compart-
ment. One check valve is located near the vacuum
fitting on the power brake booster. The second check
valve is located at the heater and air conditioner
take-out of the accessory vacuum supply line. The
vacuum check valves are designed to allow vacuum
to flow in only one direction through the accessory
vacuum supply circuits.
OPERATION
The use of the vacuum check valves help to main-
tain the system vacuum needed to retain the selected
heater-A/C mode settings. The check valves will pre-
vent the engine from bleeding down system vacuum
through the intake manifold during extended heavy
engine load (low engine vacuum) operation.
The vacuum check valves cannot be repaired and,
if faulty or damaged, they must be individually
replaced.

VACUUM RESERVOIR

DESCRIPTION
The vacuum reservoir is mounted to the underside
of the cowl plenum cover/grille panel in the right
cowl plenum area. The cowl plenum cover/grille panel
must be removed from the vehicle to access the vac-
uum reservoir for service.
HEATING AND AIR CONDITIONING
OPERATION
Engine vacuum is stored in the vacuum reservoir.
The stored vacuum is used to operate the vacuum-
controlled vehicle accessories during periods of low
engine vacuum such as when the vehicle is climbing
a steep grade, or under other high engine load oper-
ating conditions.
The vacuum reservoir cannot be repaired and, if
faulty or damaged, it must be replaced.
DIAGNOSIS AND TESTING
A/C PERFORMANCE
The air conditioning system is designed to provide
the passenger compartment with low temperature
and low humidity air. The evaporators, located in the
heater-A/C housing on the dash panel below the
instrument panel and in the rear overhead A/C unit
housing above the headliner, are cooled to tempera-
tures near the freezing point. As warm damp air
passes through the cooled evaporators, the air trans-
fers its heat to the refrigerant in the evaporator
tubes and the moisture in the air condenses on the
evaporator fins. During periods of high heat and
humidity, an air conditioning system will be more
effective in the recirculation mode (Max-A/C). With
the system in the recirculation mode, only air from
the passenger compartment passes through the evap-
orator. As the passenger compartment air dehumidi-
fies, the air conditioning system performance levels
improve.
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 air condition-
ing system. When humidity is high, the evaporator
has to perform a double duty. It must lower the air
temperature, and it must lower the temperature of
the moisture in the air that condenses on the evapo-
rator fins. Condensing the moisture in the air trans-
fers heat energy into the evaporator fins and tubing.
This reduces the amount of heat the evaporator can
absorb from the air. High humidity greatly reduces
the ability of the evaporator to lower the temperature
of the air.
However, evaporator capacity used to reduce the
amount of moisture in the air is not wasted. Wring-
ing some of the moisture out of the air entering the
vehicle adds to the comfort of the passengers.
Although, an owner may expect too much from their
air conditioning system on humid days. A perfor-
mance test is the best way to determine whether the
system is performing up to standard. This test also
provides valuable clues as to the possible cause of
trouble with the air conditioning system.
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