Jeep Cherokee 2000, Service Manual

Page: 1468 / 1528

bearing, which is part of the pulley. The compressor
clutch and coil are the only serviced parts on the
compressor.
The compressor clutch engagement is controlled by
several components: the heater-A/C mode control
switch, the low pressure cycling clutch switch, the
high pressure cut-off switch, the compressor clutch
relay, and the Powertrain Control Module (PCM).
The PCM may delay compressor clutch engagement
for up to thirty seconds. Refer to Group 14 - Fuel
System for more information on the PCM controls.
COMPRESSOR CLUTCH RELAY
DESCRIPTION
The compressor clutch relay is a International
Standards Organization (ISO) micro-relay. The termi-
nal designations and functions are the same as a con-
ventional
ISO relay. However, the micro-relay
terminal orientation (footprint) is different, the cur-
rent capacity is lower, and the relay case dimensions
are smaller than those of the conventional ISO relay.
The compressor clutch relay is located in the Power
Distribution Center (PDC) in the engine compart-
ment. Refer to the PDC label for relay identification
and location.
OPERATION
The compressor clutch relay is a electromechanical
device that switches battery current to the compres-
sor clutch coil when the Powertrain Control Module
(PCM) grounds the coil side of the relay. The PCM
responds to inputs from the heater-A/C mode control
switch, the low pressure cycling clutch switch, and
the high pressure cut-off switch. See Compressor
Clutch Relay in the Diagnosis and Testing section of
this group for more information.
The compressor clutch relay cannot be repaired
and, if faulty or damaged, it must be replaced.
CONDENSER
DESCRIPTION
The condenser is located in the air flow in front of
the engine cooling radiator. The condenser is a heat
exchanger that allows the high-pressure refrigerant
gas being discharged by the compressor to give up its
heat to the air passing over the condenser fins.
OPERATION
When the refrigerant gas gives up its heat, it con-
denses. When the refrigerant leaves the condenser, it
has become a high-pressure liquid refrigerant. The
volume of air flowing over the condenser fins is crit-
ical to the proper cooling performance of the air con-
ditioning system. Therefore, it is important that
there are no objects placed in front of the radiator
grille openings in the front of the vehicle or foreign
material on the condenser fins that might obstruct
proper air flow. Also, any factory-installed air seals or
shrouds must be properly reinstalled following radia-
tor or condenser service.
The condenser cannot be repaired and, if faulty or
damaged, it must be replaced.
DUAL FUNCTION HIGH PRESSURE SWITCH
(4.0 L)
DESCRIPTION
The Dual Function High Pressure Switch controls
both A/C clutch engagement/disengagement, and elec-
tric cooling fan operations. The 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 dual function switch is connected in series
electrically with the low pressure cycling clutch
switch 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, and
also reduces electrical surging from compressor
clutch engagement.
The dual function switch controls the electric cool-
ing fan operation by monitoring refrigerant line pres-
sures. When the discharge line pressure rises above
1900 to 2200 kPa (280 to 320 psi) the fan will turn
on. The cooling fan will turn off when the discharge
line pressure drops to 1600 kPa (235 psi).
The dual function switch controls the A/C clutch
operation by disengaging the clutch when the dis-
charge line pressure rises above 3100 to 3375 kPa
(450 to 490 psi). The switch contacts will close and
allow A/C clutch engagement when the discharge line
pressure drops to 1860 to 2275 kPa (270 to 330 psi).
The Dual Function High Pressure Switch is a fac-
tory-calibrated unit. The switch cannot be adjusted
or repaired and, if faulty or damaged, it must be
replaced.
EVAPORATOR COIL
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
24 - 4 HEATING AND AIR CONDITIONING
XJ
DESCRIPTION AND OPERATION (Continued)