2002 JEEP GRAND CHEROKEE Cooling fan

OPERATION - 3/8º PRESSURE HOSE
High pressure power steering fluid is transmitted
from the hydraulic fan motor to the steering gear by
the 3/8º steering line.
OPERATION - 3/8º GEAR OUTLET HOSE
The gear outlet hose transmits power steering fluid
under moderate low pressure to the power steering
cooler inlet tube.
OPERATION - 3/8ºRETURN HOSE
Low pressure power steering fluid is transmitted
from the steering cooler back to the power steering
pump by the 3/8º return hose.
REMOVAL
REMOVAL - 1/2(PRESSURE HOSE
(1)Drain the power steering fluid from the reservoir.
(2) Remove the air box,(Refer to 9 - ENGINE/AIR
INTAKE SYSTEM/AIR CLEANER HOUSING -
REMOVAL).
(3) Raise and support the vehicle.
(4) Remove the metal skid plate.
(5) Disconnect the high pressure hose from the
hydraulic fan motor (Fig. 8).
(6) Disconnect the high pressure hose from the
power steering pump (Fig. 8).
(7) Remove the hose from the clipped position on
the fan shroud.
(8) Remove the hose from the vehicle.
REMOVAL - 1/2(RETURN HOSE
(1) Drain the power steering fluid from the reser-
voir.
(2) Remove the air box,(Refer to 9 - ENGINE/AIR
INTAKE SYSTEM/AIR CLEANER HOUSING -
REMOVAL).
(3) Raise and support the vehicle.
(4) Remove the metal skid plate.
(5) Disconnect the rubber return hose from the
hydraulic fan motor (Fig. 9).
(6) Disconnect the rubber return hose from the
power steering reservoir .
(7) Remove the hose from the vehicle.
REMOVAL - 3/8(PRESSURE HOSE
(1) Drain the power steering fluid from the reser-
voir.
(2) Remove the air box,(Refer to 9 - ENGINE/AIR
INTAKE SYSTEM/AIR CLEANER HOUSING -
REMOVAL).
(3) Raise and support the vehicle.
(4) Remove the metal skid plate.
(5) Disconnect the high pressure hose from the
hydraulic fan motor (Fig. 10).
(6) Disconnect the high pressure hose from the
power steering gear (Fig. 10).
(7) Remove the hose from the clipped position on
the fan shroud.
(8) Remove the hose from the vehicle.
REMOVAL - 3/8(RETURN HOSE
(1) Drain the power steering fluid from the reser-
voir.
(2) Remove the air box,(Refer to 9 - ENGINE/AIR
INTAKE SYSTEM/AIR CLEANER HOUSING -
REMOVAL).
(3) Raise and support the vehicle.
(4) Disconnect the rubber hose from the steering
cooler outlet tube (Fig. 12).
Fig. 11 3/8(GEAR OUTLET HOSE
1 - HOSE CLAMP
2 - 3/89GEARR OUTLET HOSE
Fig. 12 3/8(RETURN HOSE
1 - HOSE CLAMP
2 - 3/89RETURN HOSE
3 - HYDRAULIC COOLING FAN MOTOR
WJPUMP 19 - 39
HOSES - 4.7L (Continued)

Pressure Diagnosis
Condition Possible Causes Correction
The low side pressure is
normal or slightly low, and
the high side pressure is too
low.1. Low refrigerant system
charge.1. See Plumbing/Diagnosis and Testing -
Refrigerant System Leaks in this group. Test the
refrigerant system for leaks. Repair, evacuate and
charge the refrigerant system, if required.
2. Refrigerant flow through
the accumulator is restricted.2. See Accumulator in this group. Replace the
restricted accumulator, if required.
3. Refrigerant flow through
the evaporator coil is
restricted.3. See A/C Evaporator in this group. Replace the
restricted evaporator coil, if required.
4. Faulty compressor. 4. See A/C Compressor in this group. Replace
the compressor, if required.
The low side pressure is
normal or slightly high, and
the high side pressure is too
high.1. Condenser air flow
restricted.1. Check the condenser for damaged fins, foreign
objects obstructing air flow through the condenser
fins, and missing or improperly installed air seals.
Refer to Cooling for more information on air
seals. Clean, repair, or replace components as
required.
2. Inoperative cooling fan. 2. Refer to Cooling for more information. Test the
cooling fan and replace, if required.
3. Refrigerant system
overcharged.3. See Plumbing/Standard Procedure -
Refrigerant System Charge in this group. Recover
the refrigerant from the refrigerant system.
Charge the refrigerant system to the proper level,
if required.
4. Air in the refrigerant
system.4. See Plumbing/Diagnosis and Testing -
Refrigerant System Leaks in this group. Test the
refrigerant system for leaks. Repair, evacuate and
charge the refrigerant system, if required.
5. Engine overheating. 5. Refer to Cooling for more information. Test the
cooling system and repair, if required.
The low side pressure is too
high, and the high side
pressure is too low.1. Accessory drive belt
slipping.1. Refer to Cooling for more information. Inspect
the accessory drive belt condition and tension.
Tighten or replace the accessory drive belt, if
required.
2. Faulty compressor. 2. See A/C Compressor in this group. Replace
the compressor, if required.
The low side pressure is too
low, and the high side
pressure is too high.1. Restricted refrigerant flow
through the refrigerant lines.1. See Liquid, Suction, and Discharge Line in this
group. Inspect the refrigerant lines for kinks, tight
bends or improper routing. Correct the routing or
replace the refrigerant line, if required.
2. Restricted refrigerant flow
through the a/c expansion
valve.2. See A/C Expansion Valve in this group.
Replace the Expansion Valve if restricted.
3. Restricted refrigerant flow
through the condenser.3. See A/C Condenser in this group. Replace the
restricted condenser, if required.
WJHEATING & AIR CONDITIONING 24 - 5
HEATING & AIR CONDITIONING (Continued)

DIAGNOSIS AND TESTING - HEATER
PERFORMANCE
Before performing the following tests, refer to Cool-
ing for the procedures to check the radiator coolant
level, serpentine drive belt tension, radiator air flow
and the radiator fan operation. Also be certain that
the accessory vacuum supply line is connected at the
engine intake manifold for the manual temperature
control system.
MAXIMUM HEATER OUTPUT
Engine coolant is delivered to the heater core
through two heater hoses. With the engine idling at
normal operating temperature, set the temperature
control knob in the full hot position, the mode control
switch knob in the floor heat position, and the blower
motor switch knob in the highest speed position.
Using a test thermometer, check the temperature of
the air being discharged at the HVAC housing floor
outlets. Compare the test thermometer reading to the
Temperature Reference chart.
Temperature Reference
Ambient Air Temperature15.5É C
(60É F)21.1É C
(70É F)26.6É C
(80É F)32.2É C
(90É F)
Minimum Air Temperature at
Floor Outlet62.2É C
(144É F)63.8É C
(147É F)65.5É C
(150É F)67.2É C
(153É F)
If the floor outlet air temperature is too low, refer
to Cooling to check the engine coolant temperature
specifications. Both of the heater hoses should be hot
to the touch. The coolant return heater hose should
be slightly cooler than the coolant supply heater
hose. If the return hose is much cooler than the sup-
ply hose, locate and repair the engine coolant flow
obstruction in the cooling system. Refer to Cooling
for the procedures.
OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant
flow:
²Pinched or kinked heater hoses.
²Improper heater hose routing.
²Plugged heater hoses or supply and return ports
at the cooling system connections.
²A plugged heater core.
If proper coolant flow through the cooling system is
verified, and heater outlet air temperature is still
low, a mechanical problem may exist.
MECHANICAL PROBLEMS
Possible locations or causes of insufficient heat:
²An obstructed cowl air intake.
²Obstructed heater system outlets.
²A blend door not functioning properly.
TEMPERATURE CONTROL
If the heater outlet air temperature cannot be
adjusted with the temperature control knob(s) on the
A/C Heater control panel, the following could require
service:
²The A/C heater control.
²The blend door actuator(s).
²The wire harness circuits for the A/C heater con-
trol or the blend door actuator(s).²The blend door(s).
²Improper engine coolant temperature.
STANDARD PROCEDURE - DIODE
REPLACEMENT
(1) Disconnect and isolate the negative battery
cable.
(2) Locate the diode in the harness, and remove
the protective covering.
(3) Remove the diode from the harness, pay atten-
tion to the current flow direction (Fig. 3).
(4) Remove the insulation from the wires in the
harness. Only remove enough insulation to solder in
the new diode.
Fig. 3 DIODE IDENTIFICATION
1 - CURRENT FLOW
2 - BAND AROUND DIODE INDICATES CURRENT FLOW
3 - DIODE AS SHOWN IN THE DIAGRAMS
24 - 6 HEATING & AIR CONDITIONINGWJ
HEATING & AIR CONDITIONING (Continued)

(5) Install the new diode in the harness, making
sure current flow is correct. If necessary refer to the
appropriate wiring diagram for current flow.
(6) Solder the connection together using rosin core
type solder only.Do not use acid core solder.
(7) Tape the diode to the harness using electrical
tape making, sure the diode is completely sealed
from the elements.
(8) Re-connect the battery, and test affected sys-
tems.SPECIFICATIONS
A/C APPLICATION TABLE
Item Description Notes
VEHICLE WJ - Grand
Cherokee
SYSTEM R134a w/
expansion valve
COMPRESSOR Nippondenso
10PA17ND-8 PAG oil
Freeze±up
ControlEvaporator Probe Evaporator
mounted
Low psi Control opens < 22 psi -
resets > 34-38 psi
High psi Control opens > 450-490
psi - resets <
270-330 psiline mounted
CONTROL
HEADManual type manual
controls
Automatic Zone
Control (AZC)Automatic
Zone Control
(AZC) with
dual infrared
sensing
Mode Doors Vacuum actuators
(manual)electric
actuator
(AZC)
Blend Door Electric actuator (manual and
AZC)
Blend Door
(passenger)Electric actuator (AZC only)
Recirculation
DoorVacuum actuator
(manual)electric
actuator
(AZC)
Blower Motor Hardwired to
control head
resistor block
(manual),
blower
controller (AZC)
COOLING FAN Hybrid - viscous
clutch/electricPCM output
CLUTCH
Control Relay PCM
controlled
Draw
2.0-3.9 amps @ 12 V  0.5V@ 70É F
Gap 0.0169-0.0319
DRB IIIT
Reads TPS, RPM, A/C
switch
Actuators Clutch relay
WJHEATING & AIR CONDITIONING 24 - 7
HEATING & AIR CONDITIONING (Continued)

INSTALLATION
(1) Plug the wire harness and/or vacuum harness
connectors into the back of the a/c heater control.
(2) Position the a/c heater control in the instru-
ment panel and secure it with 4 screws. Tighten the
screws to 2.2 N´m (20 in. lbs.).
(3) Reinstall the center upper, and center lower
bezels onto the instrument panel. Refer to Instru-
ment Panel System for the procedures.
(4) Connect the battery negative cable.
A/C PRESSURE TRANSDUCER
DESCRIPTION
The A/C pressure transducer is installed on a fit-
ting located on the refrigerant discharge line near
the condenser. An internally threaded hex fitting on
the transducer connects it to the externally threaded
Schrader-type fitting on the discharge line. A rubber
O-ring seals the connection between the transducer
and the discharge line fitting. Three terminals within
a molded plastic connector receptacle on the top of
the transducer connect it to the vehicle electrical sys-
tem through a take out and connector of the head-
lamp and dash wire harness.
The A/C pressure transducer cannot be adjusted or
repaired and if faulty or damaged, it must be
replaced.
OPERATION
The A/C pressure transducer monitors the pres-
sures in the high side of the refrigerant system
through its connection to a fitting on the discharge
line. The transducer will change its internal resis-
tance in response to the pressures it monitors. The
Powertrain Control Module (PCM) provides a five
volt reference signal and a sensor ground to the
transducer, then monitors the output voltage of the
transducer on a sensor return circuit to determine
refrigerant pressure. The PCM is preporgrammed to
respond to this and other sensor inputs by controlling
the operation of the air conditioning compressor
clutch and the radiator cooling fan to help optimize
air conditioning system performance and to protect
the system components from damage. The A/C pres-
sure transducer input to the PCM will also prevent
the air conditioning compressor clutch from engaging
when the ambient temperatures are below about
0.556É C (33É F) due to the pressure/temperature
relationship of the refrigerant. The Schrader-type
valve in the liquid line fitting permits the A/C pres-
sure transducer to be removed or installed without
distrubing the refrigerant in the system. The A/C
pressure transducer is diagnosed using the DRBIIIt
scan tool. Refer to the appropriate diagnostic infor-
mation.
Fig. 13 A/C HEATER CONTROL REMOVE/INSTALL
1 - MOUNTING SCREW TABS
Fig. 14 A/C HEATER CONTROL CONNECTIONS
1 - MODE SWITCH
2 - ELECTRICAL CONNECTIONS
3 - VACUUM HARNESS
WJCONTROLS 24 - 25
A/C HEATER CONTROL (Continued)

STANDARD PROCEDURE - REFRIGERANT SYS-
TEM EVACUATE)
(8) Charge the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE)
(9) Connect the negative battery cable.
A/C 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.
REMOVAL
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - WARNING) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS GROUP BEFORE
PERFORMING THE FOLLOWING OPERATION.
CAUTION: Before removing the condenser, note the
location of each of the radiator and condenser air
seals. These seals are used to direct air through the
condenser and radiator. The air seals must be rein-
stalled in their proper locations in order for the air
conditioning and engine cooling systems to per-
form as designed.(1) Disconnect and isolate the battery negative
cable.
(2) Recover the refrigerant from the refrigerant
system. (Refer to 24 - HEATING & AIR CONDI-
TIONING/PLUMBING - STANDARD PROCEDURE -
REFRIGERANT RECOVERY)
(3) Remove the screws attaching the grille and
headlamp mounting module to the upper crossmem-
ber of the vehicle. Refer to Body for this and further
steps in the procedure.
(4) Remove the headlamps from their mounts.
(5) Remove the nuts that secure the hood latch
and brace to the upper crossmember.
(6) The radiator upper crossmember can be
adjusted left or right through the use of its slotted
mounting holes. Before removal, mark the original
position of the crossmember.
(7) Remove the bolts that secure the radiator to
the upper crossmember and set it aside (Fig. 6).
(8) Remove the engine air filter inlet duct secured
at the headlamp mounting module.
(9) Remove the headlamp mounting module and
front fascia for access to the condenser and fittings.
(10) Disconnect the discharge line and liquid line
refrigerant line fittings from the condenser. Install
plugs in, or tape over all of the opened refrigerant
line fittings.Fig. 6 CONDENSER MOUNTING - TYPICAL
1 - CONDENSER-TO-RADIATOR MOUNTING BRACKETS (2)
2 - UPPER CROSSMEMBER
3 - FAN SHROUD
4 - ALIGNMENT TABS
5 - RADIATOR
6 - ALIGNMENT DOWELS (2)
7 - RUBBER ISOLATORS (2)
8 - RUBBER GROMMETS (2)
9 - LOWER CROSSMEMBER
10 - CONDENSER
24 - 62 PLUMBINGWJ
A/C COMPRESSOR (Continued)

VISCOUS HEATER
DESCRIPTION
DESCRIPTION
The diesel engine has an engine mounted mechan-
ical device called a Viscous Heater that is used to
heat the coolant coming from the engine to the
heater core. The Viscous Heater is driven by the
engine fan belt and has a electro-mechanical clutch
which is controlled by the HVAC control unit.
DESCRIPTION - VISCOUS HEATER CLUTCH
The basic viscous heater clutch assembly consists
of a stationary electromagnetic coil, a hub bearing
and pulley assembly and a clutch plate. The electro-
magnetic coil unit and the hub bearing and pulley
assembly are each retained on the nose of the com-
pressor front housing with snap rings (Fig. 17). The
clutch plate is keyed to the viscous heater shaft and
secured with a nut. These components provide the
means to engage and disengage the viscous heater
from the engine accessory drive belt.
OPERATION
OPERATION - VISCOUS HEATER
The Viscous Heater is driven by the engine fan
belt. The Viscous Heater has an electro-mechanical
clutch that receives a signal from the HVAC control
head and the Viscous Heater controller that ener-
gizes and engages the clutch. Once engaged theclutch allows the Viscous Heater to increase the tem-
perature of the coolant flowing to the heater core,
which provides heat the passenger compartment
quicker than normal engines without the Viscous
Heater. The Viscous Heater generates heat by means
of friction which heats a special Silicon Oil within its
housing which is then transferred to the engine cool-
ant when the coolant passes over fins within the
pump. Please note that the coolant is isolated from
the silicon oil within the pump housing. When
demand for passenger compartment heat decreases
the Viscous Heater clutch will receive an input from
the Viscous heater controller to disengage.
OPERATION - VISCOUS HEATER CLUTCH
When the clutch coil is energized, it magnetically
draws the clutch into contact with the pulley and
drives the viscous heater shaft. When the coil is not
energized the pulley freewheels on the clutch hub
bearing, which is part of the pulley. The viscous
heater clutch and coil are the only serviced parts on
the viscous heater assembly. If the viscous heater is
inoperative or damaged the entire assembly must be
replaced. The viscous heater clutch engagement is
controlled by several components: the viscous heater
controller, the engine powertrain control module and
the HVAC control head.
REMOVAL
REMOVAL - VISCOUS HEATER
(1) Drain the engine coolant(Refer to 7 - COOL-
ING/ENGINE - STANDARD PROCEDURE).
(2) Remove the engine accessory drive belt(Refer to
7 - COOLING/ACCESSORY DRIVE/DRIVE BELTS -
REMOVAL).
(3) Remove the heater hose clamps at the Viscous
Heater.
(4) Remove the heater hoses from the Viscous
Heater.
(5) Unplug the Viscous Heater clutch electrical
connector.
(6) Remove the bolts holding the Viscous Heater to
the mounting bracket.
(7) Remove the Viscous Heater from the vehicle.
REMOVAL - VISCOUS HEATER CLUTCH
(1) The viscous heater clutch can be serviced in
the vehicle and the cooling system does not have to
be drained.
(2) Disconnect and isolate the battery negative
cable.
(3) Remove the serpentine drive belt(Refer to 7 -
COOLING/ACCESSORY DRIVE/DRIVE BELTS -
REMOVAL).
Fig. 17 CLUTCH ASSEMBLY- typical
1 - CLUTCH PLATE
2 - SHAFT KEY
3 - PULLEY
4 - COIL
5 - CLUTCH SHIMS
6 - SNAP RING
7 - SNAP RING
24 - 76 PLUMBINGWJ

(M)Malfunction Indicator Lamp (MIL) illuminated during engine operation if this DTC was recorded
(depending if required by CARB and/or EPA). MIL is displayed as an engine icon on instrument panel.
(G)Generator lamp illuminated
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P1498 High Speed Rad Fan Ground CTRL
Rly CircuitAn open or shorted condition detected in the control
circuit of the #3 high speed radiator fan control relay.
P1499 Hydraulic cooling fan solenoid circuit An open or shorted condition detected in the cooling fan
control solenoid circuit.
P1594 (G) Charging System Voltage Too High Battery voltage sense input above target charging voltage
during engine operation.
P1594 Charging System Voltage Too High Battery voltage sense input above target charging voltage
during engine operation.
P1595 Speed Control Solenoid Circuits An open or shorted condition detected in either of the
speed control vacuum or vent solenoid control circuits.
P1595 Speed Control Solenoid Circuits An open or shorted condition detected in the speed
control vacuum or vent solenoid circuits.
P1596 Speed Control Switch Always High Speed control switch input above maximum acceptable
voltage.
P1597 Speed Control Switch Always Low Speed control switch input below minimum acceptable
voltage.
P1597 Speed Control Switch Always Low Speed control switch input below the minimum acceptable
voltage.
P1598 A/C Pressure Sensor Volts Too High A/C pressure sensor input above maximum acceptable
voltage.
P1598 A/C Sensor Input Hi Problem detected in air conditioning electrical circuit.
P1599 A/C Pressure Sensor Volts Too Low A/C pressure sensor input below minimum acceptable
voltage.
P1599 A/C Sensor Input Lo Problem detected in air conditioning electrical circuit.
P1602 PCM not programmed
P1680 Clutch Released Switch Circuit Problem detected in clutch switch electrical circuit.
P1681 No I/P Cluster CCD/J1850
Messages ReceivedNo CCD/J1850 messages received from the cluster
control module.
P1682 (G) Charging System Voltage Too Low Battery voltage sense input below target charging voltage
during engine operation and no significant change in
voltage detected during active test of generator output
circuit.
P1682 Charging System Voltage Too Low Charging system output voltage low.
P1683 SPD CTRL PWR Relay; or S/C 12v
Driver CKTAn open or shorted condition detected in the speed
control servo power control circuit.
P1683 Spd ctrl pwr rly, or s/c 12v driver
circuitAn open or shorted condition detected in the speed
control servo power control circuit.
P1684 Batt Loss (disconnected) in last 50
StartsThe battery has been disconnected within the last 50
starts
P1685 SKIM Invalid Key - (Wrong or Invalid
Key MSG Received From SKIM)The engine controler has received an invalid key from the
SKIM.
P1686 No SKIM BUS Messages Received No CCD/J1850 messages received from the Smart Key
Immobilizer Module (SKIM).
25 - 14 EMISSIONS CONTROLWJ
EMISSIONS CONTROL (Continued)