1988 JEEP CHEROKEE heater

GEN ER AL C O OLIN G S YSTE M S ER VIC IN G

1988 J e ep C hero ke e
GENERAL INFORMATION
General Cooling System Servicing
* PLEASE READ THIS FIRST *
The following article is for general information only.
Information may not apply to all years, makes and models. See specific
article in the ENGINE COOLING section.
DESCRIPTION
The basic liquid cooling system consists of a radiator, water
pump, thermostat, electric or belt-driven cooling fan, pressure cap,
heater, and various connecting hoses and cooling passages in the block
and cylinder head.
MAINTENANCE
DRAINING
Remove radiator cap and open heater control valve to maximum
heat position. Open drain cocks or remove plugs in bottom of radiator
and engine block. In-line engines usually have one plug or drain cock,
while "V" type engines will have 2, one in each bank of cylinders.
CLEANING
A good cleaning compound removes most rust and scale. Follow
manufacturer's instructions in the use of cleaner. If considerable
rust and scale has to be removed, cooling system should be flushed.
Clean radiator air passages with compressed air.
FLUSHING
CAUTION: Some manufacturers use an aluminum and plastic radiator.
Flushing solution must be compatible with aluminum.
Back Flushing
Back flushing is an effective means of removing cooling
system rust and scale. The radiator, engine and heater core should be
flushed separately.
Radiator
To flush radiator, connect flushing gun to water outlet of
radiator and disconnect water inlet hose. To prevent flooding engine,
use a hose connected to radiator inlet. Use air in short bursts to
prevent damage to radiator. Continue flushing until water runs clear.
Engine
To flush engine, remove thermostat and replace housing.
Connect flushing gun to water outlet of engine. Flush using short air
bursts until water runs clean.
Heater Core
Flush heater core as described for radiator. Ensure heater
control valve is set to maximum heat position before flushing heater.

HEA TE R S YSTE M T R O UBLE S H O OTIN G

1988 J e ep C hero ke e
1989 HEATER SYSTEMS
Eagle Trouble Shooting
CONDITION & POSSIBLE CAUSE
Little or No Air From Heater Floor Outlets.
* Misadjusted heater air door cable.
* Obstructed heater housing or ducts.
* Clogged heater core fins.
* Leaking air duct seals.
Little or No Air From Defroster Outlets.
* Defroster duct misaligned.
* Defroster cable incorrectly adjusted
* Leaking air duct seals.
* Defroster duct damaged.
Heat Output When Controls Are Off.
* Outside air cable misadjusted
* Outside Air door binding in housing.
Not Enough Heat With Controls Fully On.
* Low coolant or plugged heater core.
* Incorrect thermostat.
* Incorrect adjustment of cables.
* Heater System Air Leaks.
* Blend air door not in proper position.
Blower Will Not Run.
* Blown fuse.
* Loose connections or poor ground.
* Faulty switch, motor or resistor.
Blower Runs But Does Not Circulate Air.
* Intake blocked..
* Fan not attached to motor shaft.

HEA TE R S YSTE M

1988 J e ep C hero ke e
1988 HEATER SYSTEMS
Jeep
DESCRIPTION
Jeep vehicles use a blend-air type heater system. Wrangler
models have a constant flow type system with engine coolant
continuously flowing through heater core. Cherokee and Comanche use
heater control valves. Coolant flow to heater core on these models can
be stopped or diverted.
On all models, temperature of heated air entering passenger
compartment is controlled by regulating amount of air flowing through
heater core and then blending it with a controlled amount of cool air
by-passing heater core.
CONTROL PANEL OPERATION
Control panel on all models includes fan switch, sliding
temperature control lever and sliding mode lever.
DEFROSTER CONTROL
Defroster control operates heater housing door regulating
heater and defroster operation by directing flow of air through
defroster hose or floor outlets. When control knob is pushed in,
blended air will enter passenger compartment through floor heat duct.
When control is pulled completely out, door directs all heated air to
windshield defroster outlets. Any intermediate position divides air
flow between windshield and floor outlets.
TEMPERATURE CONTROL LEVER (CHEROKEE, COMANCHE & WRANGLER)
Lower control lever operates blend-air door in heater core
housing. At full right position, all air is directed through heater
core, providing maximum heat flow. At full left position, all air is
directed around heater core providing fresh air. Control can be set in
any intermediate position to provide a blend of heated and unheated
air. With control lever in "COOL" position, water valve will close
(except Wrangler). Mode control lever must be in "HEAT" or defroster
mode before any air can enter vehicle.
MODE CONTROL LEVER (CHEROKEE & COMANCHE)
Mode control lever includes "BI-LEVEL", "VENT", "HEAT" and
"OFF" positions. At far end of scale, a symbol for defroster indicates
defrost position. In "BI-LEVEL" position, a mixture of floor heat and
defroster air is obtained.
FAN CONTROL
Fan control is a 4-position control switch, regulating blower
motor and air flow for heat and defrost. Switch has "LOW", "HIGH" and
2 intermediate positions. Fan will remain on unless mode lever is
placed in "OFF" position.
CONTROL CABLES ADJUSTMENT

CHEROKEE & COMANCHE
The heater control cable is retained to blend air door lever
with a retaining clip and a self-adjusting clip. During installation,
self-adjusting clip will locate cable properly when cable is snapped
into position on lever.
WRANGLER
The only adjustable cables are the vent door control cables.
Since the left cable operates the right cable, the cables must be
installed and adjusted in the proper order to maintain the self
adjusting mechanism.
With cables connected to heater control panel, connect only
the right vent door cable. Open and close right vent door one time,
using heater control panel. Connect left side cable and ensure that
both vent doors open at the same time.
Fig. 1: Heater & Defroster Components (Wrangler)
Courtesy of Chrysler Motors.

Fig. 2: Typical Heater & Defroster Components
Courtesy of Chrysler Motors.
BLOWER MOTOR R & I
NOTE: On Cherokee and Comanche, blower motor and fan are removed
from engine compartment.
Removal & Installation
1) Remove heater core housing assembly. On all models, remove
blower motor electrical connectors. Detach screws retaining blower
motor assembly to heater housing. Remove blower motor and fan
assembly. On Cherokee and Comanche, detach fan retaining clip from fan
hub, if necessary. Remove fan from motor shaft.
2) To install, reverse removal procedure. If removed, ensure
ears of retaining clip are over flat surface on motor shaft. Check
blower motor and heater operation.
CONTROL PANEL R & I
Removal & Installation
1) Disconnect battery ground. On Cherokee, remove lower
instrument panel. On all models, remove instrument panel bezel. On
Cherokee, remove clock and radio (if equipped).
2) On all models, remove heater control panel attaching
screws. Pull out control panel and disconnect vacuum hoses, wires and
cables. Note locations for reassembly reference. Remove control panel.
To install, reverse removal procedure.
CONTROL CABLES R & I
REMOVAL (CHEROKEE & COMANCHE)
Remove control panel. Detach cable from heater control panel.

Remove retaining clip and cable self-adjusting clip from blend-air
door lever at bottom of blower housing. Remove cable by squeezing tabs
with needle nose pliers. Do not break housing.
INSTALLATION
To install, connect cable self-adjusting clip to blend-air
door lever, then snap cable into position. Install retaining clip onto
blend-air door lever. Route cable to A/C-heater control panel and
connect. Install control panel.
REMOVAL & INSTALLATION (WRANGLER)
1) Disconnect cables from vent doors. Disconnect cables from
heater control panel levers. Remove cables by squeezing tabs with
needle nose pliers.
2) Connect and adjust cables as described in ADJUSTMENTS
section of this article
HEATER CORE R & I
REMOVAL & INSTALLATION (CHEROKEE & COMANCHE)
1) Disconnect battery ground. Drain cooling system.
Disconnect heater hoses at heater core inlet and outlet tubes.
Disconnect blower motor wires and vent tube. Remove console (if
equipped). Remove lower instrument panel.
2) Disconnect electrical connectors from blower motor
resistors. Disconnect vacuum hose at vacuum motor. Cut plastic
retaining strap holding blower housing to heater core housing.
3) Disconnect and remove heater control cable. Detach clip at
rear of blower housing flange and remove retaining screws. Remove
housing mounting nuts from studs on engine compartment side of dash
panel. Remove right kick panel.
4) Remove instrument panel support bolt. Gently pull on right
side of dash, then rotate housing downward and toward rear of vehicle
to disengage housing studs from dash panel. Remove blower housing.
Detach retaining screws and remove heater core by pulling it straight
out of housing.
5) To install, reverse removal procedure. Ensure seal is
cemented in place to prevent movement when blower assembly is
installed. Connect heater hoses and fill cooling system.
REMOVAL & INSTALLATION (WRANGLER)
1) Disconnect battery ground. Drain about 2 quarts of coolant
from radiator. Disconnect heater hoses at heater core inlet and outlet
tubes. Disconnect vent door cables. Disconnect blower motor wires.
Disconnect defroster duct.
2) Remove nuts attaching heater housing studs to engine
compartment side of dash panel. Remove heater housing assembly by
tilting it downward, to disengage it from defroster duct.
3) Pull heater housing rearward and out from under instrument
panel. Remove heater housing cover from heater housing assembly.
Remove heater core from housing.
HEATER SYSTEM OPREATION CHART & VACUUM DIAGRAM
HEATER SYSTEM OPERATION TABLE







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MODE       

 LEVER   BLOWER  PANEL  FLOOR  DEFROST  WATER 


POSITION AIR DISCHARGE SPEEDS  DOOR  DOOR  DOOR  VALVE 










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Off  Closed  None  Closed Closed Closed  Closed 










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Vent  Panel  4  Open  Closed Closed  Closed 

 Registers      










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Bi-Level  Panel  4  Open  Open  Bleed  Open
(1)

 Registers      

 and Floor      

 With Def.      

 Bleed      










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Heat  Floor With  4  Closed Open  Bleed  Open
(1)

 Def. Bleed      










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Def.  Defroster  4  Closed Closed Open  Open
(1)

      










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(1)
- Water valve closes in full "COOL" temperature lever position. 










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Fig. 3: Heater Control System Vacuum Diagram

WIRING DIAGRAMS

Fig. 4: Heater Wiring Diagram (Comanche Diesel)