Refrigerant System Service Port; Vacuum Check Valve; Diagnosis And Testing; A/C Performance - Jeep cherokee 2000 Service Manual

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DESCRIPTION AND OPERATION (Continued)
oil can cause compressor damage, and too much can
reduce air conditioning system performance.
PAG refrigerant oil is much more hygroscopic than
mineral oil, and will absorb any moisture it comes
into contact with, even moisture in the air. The PAG
oil container should always be kept tightly capped
until it is ready to be used. After use, recap the oil
container immediately to prevent moisture contami-
nation.

REFRIGERANT SYSTEM SERVICE PORT

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
refrigerant line, near the discharge port of the com-
pressor. The low pressure service port is located on
the liquid line at the rear of the engine compartment,
near the evaporator inlet tube.
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
A vacuum check valve is installed in the accessory
vacuum supply line in the engine compartment, near
the vacuum tap on the engine intake manifold, and
at the HVAC unit takeout. The vacuum check valve
is designed to allow vacuum to flow in only one direc-
tion through the accessory vacuum supply circuits.
OPERATION
The use of a vacuum check valve helps to maintain
the system vacuum needed to retain the selected
heater-A/C mode settings. The check valve 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 valve cannot be repaired and, if
faulty or damaged, it must be replaced.
HEATING AND AIR CONDITIONING
VACUUM RESERVOIR
DESCRIPTION
The vacuum reservoir is mounted to the front
bumper bar behind the passenger side bumper end
cap. The bumper end cap must be removed from the
vehicle to access the vacuum reservoir for service.
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 evaporator, located in the
heater-A/C 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 dehu-
midifies, 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.
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