Jeep Cherokee 2000, Service Manual

Page: 1469 / 1528

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 fixed
orifice tube as a low-temperature, low-pressure liq-
uid. 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 vapor-
ize. 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.
FIXED ORIFICE TUBE
DESCRIPTION
The fixed orifice tube is installed in the liquid line
(left-hand drive) or liquid line jumper (right-hand
drive) between the outlet of the condenser and the
inlet of the evaporator. The fixed orifice tube is
located in the end of the liquid line or liquid line
jumper that is closest to the condenser outlet tube.
The inlet end of the fixed orifice tube has a nylon
mesh filter screen, which filters the refrigerant and
helps to reduce the potential for blockage of the
metering orifice by refrigerant system contaminants
(Fig. 3). The outlet end of the tube has a nylon mesh
diffuser screen. The O-rings on the plastic body of
the fixed orifice tube seal the tube to the inside of
the liquid line and prevent the refrigerant from
bypassing the fixed metering orifice.
OPERATION
The fixed orifice tube is used to meter the flow of
liquid refrigerant into the evaporator coil. The high-
pressure liquid refrigerant from the condenser
expands into a low-pressure liquid as it passes
through the metering orifice and diffuser screen of
the fixed orifice tube.
The fixed orifice tube cannot be repaired and, if
faulty or plugged, the liquid line and fixed orifice
tube unit or liquid line jumper and fixed orifice tube
unit 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. On heater-only systems, the evaporator
coil and recirculating air door are omitted from the
housing.
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
Fig. 3 Fixed Orifice Tube - Typical
1 – DIFFUSER SCREEN
2 – “O” RINGS
3 – INLET FILTER SCREEN
4 – ORIFICE
Fig. 4 Common Blend-Air Heater-Air Conditioner
System - Typical
1 – HEATER CORE
2 – BLEND-AIR DOOR
3 – EVAPORATOR A/C ONLY
4 – RECIRCULATING AIR DOOR A/C ONLY
5 – FLOOR/PANEL DOOR
6 – FLOOR/DEFROST DOOR
XJ
HEATING AND AIR CONDITIONING 24 - 5
DESCRIPTION AND OPERATION (Continued)