2002 JEEP GRAND CHEROKEE All wheel drive

panel steering column support bracket. (Refer to 8 -
ELECTRICAL/POWER DISTRIBUTION/JUNCTION
BLOCK - INSTALLATION).
(7) Position the 16-way data link connector to the
instrument panel steering column support bracket.
(8) Install and tighten the two screws that secure
the 16-way data link connector to the instrument
panel steering column support bracket. Tighten the
screws to 2.2 N´m (20 in. lbs.).
(9) Reinstall the instrument cluster onto the
instrument panel. (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - INSTALLATION).
(10) Reconnect the battery negative cable.
INSTRUMENT PANEL TRIM
BEZEL - DRIVER
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Using a trim stick or another suitable wide
flat-bladed tool, gently pry the edges of the driver
side trim bezel up and away from the instrument
panel far enough to disengage the two snap clips
from their receptacles (Fig. 36).
(3) Remove the driver side trim bezel from the
instrument panel top pad.
INSTALLATION
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Position the driver side trim bezel to the
instrument panel top pad.
(2) Align the snap clips on the driver side trim
bezel with the receptacles in the instrument panel
top pad.
(3) Using hand pressure, press firmly and evenly
on the driver side trim bezel over the snap clip loca-
tions until each of the snap clips is fully engaged in
its receptacle.
(4) Reconnect the battery negative cable.
Fig. 36 Instrument Panel Driver Side Trim Bezel
Remove/Install
1 - INSTRUMENT PANEL TOP PAD
2 - DRIVER SIDE TRIM BEZEL
3 - TRIM STICK
4 - PANEL OUTLET
WJINSTRUMENT PANEL SYSTEM 23 - 65
INSTRUMENT PANEL STEERING COLUMN SUPPORT BRACKET (Continued)

STEERING COLUMN OPENING
COVER
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the fuse cover from the Junction Block
(JB) and Body Control Module (BCM) unit under the
driver side outboard end of the instrument panel.
(Refer to 8 - ELECTRICAL/POWER DISTRIBU-
TION/FUSE COVER - REMOVAL).
(3) Remove the cluster bezel from the instrument
panel. (Refer to 23 - BODY/INSTRUMENT PANEL/
CLUSTER BEZEL - REMOVAL).
(4) Remove the one screw that secures the out-
board end of the steering column opening cover to
the U-nut on the outboard end of the instrument
panel top pad (Fig. 39).
(5) Remove the two screws that secure the lower
edge of the steering column opening cover to the
U-nuts on the instrument panel steering column sup-
port bracket.
(6) Pull the steering column opening cover rear-
ward to disengage the three snap clips (one outboard
and two inboard) that secure it to the receptacles in
the instrument panel.
(7) Remove the steering column opening cover
from the instrument panel.
INSTALLATION
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THISIS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Position the steering column opening cover
onto the instrument panel (Fig. 39).
(2) Align the three snap clips on the steering col-
umn opening cover with their receptacles in the
instrument panel.
(3) Using hand pressure, press firmly and evenly
on the steering column opening cover over the snap
clip locations until each of the snap clips is fully
engaged in its receptacle.
(4) Install and tighten the two screws that secure
the lower edge of the steering column opening cover
to the instrument panel steering column support
bracket. Tighten the screws to 2.2 N´m (20 in. lbs.).
(5) Install and tighten the one screw that secures
the outboard end of the steering column opening
cover to the U-nut on the outboard end of the instru-
ment panel top pad. Tighten the screw to 2.2 N´m (20
in. lbs.).
(6) Reinstall the cluster bezel onto the instrument
panel. (Refer to 23 - BODY/INSTRUMENT PANEL/
CLUSTER BEZEL - INSTALLATION).
(7) Reinstall the fuse cover onto the Junction
Block (JB) and Body Control Module (BCM) unit
under the driver side outboard end of the instrument
panel. (Refer to 8 - ELECTRICAL/POWER DISTRI-
BUTION/FUSE COVER - INSTALLATION).
(8) Reconnect the battery negative cable.
Fig. 39 Steering Column Opening Cover Remove/
Install
1 - INSTRUMENT PANEL TOP PAD
2 - STEERING COLUMN OPENING COVER
3 - SCREW (3)
23 - 68 INSTRUMENT PANEL SYSTEMWJ

A/C COMPRESSOR CLUTCH
DESCRIPTION
The compressor clutch assembly consists of a sta-
tionary electromagnetic coil, a hub bearing and pul-
ley assembly, and a clutch plate (Fig. 4). The
electromagnetic coil unit and the hub bearing and
pulley assembly are each retained on the nose of the
compressor front housing with snap rings. The clutch
plate is keyed to the compressor shaft and secured
with a bolt.
OPERATION
The compressor clutch components provide the
means to engage and disengage the compressor from
the engine serpentine accessory drive belt. When the
clutch coil is energized, it magnetically draws the
clutch into contact with the pulley and drives the
compressor shaft. When the coil is not energized, the
pulley freewheels on the clutch hub 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 a/c switch on the a/c heater
control panel, the Automatic Zone Control (AZC) con-
trol module (if the vehicle is so equipped), the evap-
orator probe, the a/c high pressure transducer, the
a/c compressor clutch relay, the body control module
(BCM) and the Powertrain Control Module (PCM).
The PCM may delay compressor clutch engagement
for up to thirty seconds. Refer to Electronic Control
Modules for more information on the PCM controls.
DIAGNOSIS AND TESTING - COMPRESSOR
CLUTCH COIL
For circuit descriptions and diagrams, refer to the
appropriate wiring diagrams. The battery must be
fully-charged before performing the following tests.
Refer to Battery for more information.
(1) Connect an ammeter (0 to 10 ampere scale) in
series with the clutch coil terminal. Use a voltmeter
(0 to 20 volt scale) with clip-type leads for measuring
the voltage across the battery and the compressor
clutch coil.
(2) With the a/c heater mode control switch in any
a/c mode, the a/c heater control a/c switch in the ON
position, and the blower motor switch in the lowest
speed position, start the engine and run it at normal
idle.
(3) The compressor clutch coil voltage should read
within 0.2 volts of the battery voltage. If there is
voltage at the clutch coil, but the reading is not
within 0.2 volts of the battery voltage, test the clutch
coil feed circuit for excessive voltage drop and repair
as required. If there is no voltage reading at the
clutch coil, use a DRBIIItscan tool and the appro-
priate diagnostic information for testing of the com-
pressor clutch circuit. The following components
must be checked and repaired as required before you
can complete testing of the clutch coil:
²Fuses in the junction block and the Power Dis-
tribution Center (PDC)
²A/C heater mode control switch
²A/C compressor clutch relay
²A/C high pressure transducer
²A/C evaporator probe
²Powertrain Control Module (PCM)
²Body Control Module (BCM)
(4) The compressor clutch coil is acceptable if the
current draw measured at the clutch coil is 2.0 to 3.9
amperes with the electrical system voltage at 11.5 to
12.5 volts. This should only be checked with the work
area temperature at 21É C (70É F). If system voltage
is more than 12.5 volts, add electrical loads by turn-
ing on electrical accessories until the system voltage
drops below 12.5 volts.
(a) If the clutch coil current reading is four
amperes or more, the coil is shorted and should be
replaced.
(b) If the clutch coil current reading is zero, the
coil is open and should be replaced.
Fig. 4 COMPRESSOR CLUTCH - TYPICAL
1 - CLUTCH PLATE
2 - SHAFT KEY
3 - PULLEY
4 - COIL
5 - CLUTCH SHIMS
6 - SNAP RING
7 - SNAP RING
WJCONTROLS 24 - 13

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Check for battery voltage at the fuse in the
Power Distribution Center (PDC). If OK, go to Step
2. If not OK, repair the shorted circuit or component
as required and replace the faulty fuse.
(2) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Remove the a/c heater control from the instrument
panel. (Refer to 24 - HEATING & AIR CONDITION-
ING/CONTROLS/A/C HEATER CONTROL -
REMOVAL) Check for continuity between the ground
circuit cavity of the a/c heater control wire harness
connector and a good ground. There should be conti-
nuity. If OK, go to Step 3. If not OK, repair the open
circuit to ground as required.
(3) With the a/c heater control wire harness con-
nector unplugged, place the a/c heater mode control
switch knob in any position except the Off position.
Check for continuity between the ground circuit ter-
minal and each of the blower motor driver circuit ter-
minals of the a/c heater control as you move the
blower motor switch knob to each of the four speed
positions. There should be continuity at each driver
circuit terminal in only one blower motor switch
speed position. If OK, test and repair the blower
driver circuits between the a/c heater control connec-
tor and the blower motor resistor as required. If not
OK, replace the faulty a/c heater control unit.
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTALAIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
The blower motor switch cannot be adjusted or
repaired, and if faulty or damaged, the a/c heater
control must be replaced. (Refer to 24 - HEATING &
AIR CONDITIONING/CONTROLS/A/C HEATER
CONTROL - REMOVAL)
IN-CAR TEMPERATURE
SENSOR
DESCRIPTION
Models equipped with the optional Automatic Zone
Control (AZC) system use automatic dual zone tem-
perature control with infrared sensing technology.
The temperature sensor is located in the center
instrument panel, between the dual temperature
knobs of the AZC.
OPERATION
The Automatic Zone Control uses infrared sensing
technology to control occupant comfort levels, not the
actual passenger compartment air temperature. Dual
infrared sensors mounted in the face of the control
unit independently measure the surface temperature
to maintain customer-perceived comfort temperature
under changing conditions. Dual Zone temperature
control provides wide side-to-side variation in comfort
temperature to exceed the needs of either front seat
occupant. This sensing system replaces interior air
temperature and solar sensors used to approximate
direct sensing control through complex control pro-
grams.
The infrared temperature sensor cannot be
adjusted or repaired and, if faulty or damaged, the
AZC head must be replaced.
NOTE: The infrared sensor window may be perma-
nently damaged if any type of cosmetic vinyl dress-
ings are allowed to contact the lens. Avoid spraying
or wiping this area with any cleaner or conditioner.
This may result in impaired temperature sensing
and control.
REMOVAL
The infrared temperature sensor cannot be
adjusted or repaired and, if faulty or damaged, the
AZC head must be replaced. (Refer to 24 - HEATING
& AIR CONDITIONING/CONTROLS/A/C HEATER
CONTROL - REMOVAL)
WJCONTROLS 24 - 29
BLOWER MOTOR SWITCH (Continued)

BLEND DOOR ACTUATOR
DESCRIPTION
The blend door for all models is actuated by an
electric actuator, while the AZC system uses 2 sepa-
rate actuators to allow the driver and passenger to
select individual comfort levels. In the following pro-
cedures, service for both types of actuators is cov-
ered.
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
The blend door actuator is used on all models,
whether equipped with manual or Automatic Zone
Control (AZC). This actuator is located on the front of
the HVAC housing to the right of the floor panel
transmission tunnel, and can be removed from the
passenger compartment without instrument panel or
HVAC housing removal.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the glove box door. Refer to Instrument
Panel System for the procedures.
(3) Remove the lower I/P glove box door surround
panel. Refer to Instrument Panel System for the pro-
cedures.
(4) Unplug the wire harness connector from the
blend door actuator (Fig. 17).
(5) Remove the 2 screws that secure the blend
door actuator to the HVAC housing.
(6) Remove the blend door actuator from the
HVAC housing.
INSTALLATION
(1) Install the blend door actuator on the HVAC
housing and tighten the two mounting screws to 2.2
N´m (20 in. lbs.).
(2) Plug in the wire harness connector to the blend
door actuator.
(3) Install the glove box door. Refer to Instrument
Panel System for the procedures.
(4) Install the lower I/P glove box door surround
panel. Refer to Instrument Panel System for the pro-
cedures.
(5) Connect and the battery negative cable.
MODE DOOR ACTUATOR
DESCRIPTION
The mode door actuators for vehicles equipped with
the standard equipment manual temperature control
system are vacuum controlled. The optional Auto-
matic Zone Control (AZC) system uses electric motors
to actuate all mode doors. The service procedures for
both types of actuators are covered by the following
procedures.
Fig. 17 BLEND DOOR ACTUATOR
1 - BLEND DOOR ACTUATOR
2 - ELECTRICAL CONNECTOR
24 - 30 CONTROLSWJ

(1) Disconnect and isolate the battery negative
cable.
(2) Pinch the connector retainer and unplug the
blower motor wire harness from the blower motor
(Fig. 2).
(3) Remove the three screws that secure the
blower motor and blower wheel assembly to the
HVAC housing, using either a T-25 Torxthead or
flat-bladed screwdriver.
(4) Lower the blower motor and wheel from the
HVAC housing.
(5) Remove the blower wheel retainer clip (Fig. 3).
(6) Remove the wheel from the blower motor shaft.
INSTALLATION
(1) Press the blower wheel hub onto the blower
motor shaft. Be sure the flat on the blower motor
shaft is indexed to the flat on the inside of the blower
wheel hub.
(2) Install the retainer clip over the blower wheel
hub.
(3) Install the blower motor in the HVAC housing
with three mounting screws. Tighten the mounting
screws to 2.2 N´m (20 in. lbs.).
(4) Plug the blower motor wire harness connector
into the blower motor socket.
(5) Connect the battery negative cable.
DEFROSTER DUCTS
REMOVAL
(1) Remove the instrument panel assembly from
the vehicle(Refer to 23 - BODY/INSTRUMENT
PANEL - REMOVAL).
(2) Remove the three screws that secure the
defroster duct to the HVAC unit housing (Fig. 4).
(3) Remove the defroster duct from the HVAC unit
housing.
Fig. 2 BLOWER MOTOR (HOUSING REMOVED
FROM VEHICLE)
1 - BLOWER MOTOR RESISTOR
2 - BLOWER MOTOR
3 - GROUND STRAP
4 - ELECTRICAL CONNECTORS
5 - HEATER CORE TUBES
Fig. 3 BLOWER MOTOR WHEEL REMOVE/INSTALL
1 - BLOWER MOTOR WHEEL
2 - RETAINER CLIP
Fig. 4 HVAC DEFROSTER DUCT
1 - HVAC UNIT HOUSING
2 - INSTRUMENT PANEL
3 - SCREWS
4 - DEFROSTER DUCT
24 - 38 DISTRIBUTIONWJ
BLOWER MOTOR (Continued)

STANDARD PROCEDURE - REFRIGERANT SYS-
TEM EVACUATE)
(13) Charge the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE)
(14) Install the instrument panel in the vehicle(Re-
fer to 23 - BODY/INSTRUMENT PANEL - INSTAL-
LATION).
(15) Connect the battery negative cable.
(16) Start the engine and check for proper opera-
tion of the heating and air conditioning systems.
BLEND DOOR
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Remove and disassemble the HVAC housing.
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - REMOVAL)
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - DISASSEMBLY)
(2) Remove evaporator from lower case to ease
access to plastic door shaft bushing.
(3) Pinch the retention tabs holding the blend door
pivot shaft to the case. The 3 plastic tabs, located on
the inside of the case, are part of the shaft retainer.
(4) Remove door(s).
INSTALLATION
(1) Install the blend door(s) by snapping the pivot
shaft into the HVAC case.
(2) Install the evaporator in the lower case.
(3) Reassemble the HVAC housing and install in
the vehicle. (Refer to 24 - HEATING & AIR CONDI-
TIONING/DISTRIBUTION/HVAC HOUSING -
ASSEMBLY) (Refer to 24 - HEATING & AIR CON-
DITIONING/DISTRIBUTION/HVAC HOUSING -
INSTALLATION)NOTE: The blend door sub-assembly is attached to
the housing with 2 screws, and may be removed for
service (Fig. 20).
MODE DOOR
REMOVAL
REMOVAL - PANEL OUTLET DOOR
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Remove and disassemble the HVAC housing.
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - REMOVAL)
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - DISASSEMBLY)
Fig. 20 BLEND DOOR SUB-ASSEMBLY
1 - PASSENGER SIDE BLEND DOOR
2 - BLEND DOOR SUB-ASSEMBLY
3 - DOOR PIVOT SHAFT BUSHING
4 - DOOR SHAFT LEVER
5 - DRIVER SIDE BLEND DOOR
24 - 46 DISTRIBUTIONWJ
HVAC HOUSING (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