heating JEEP CHEROKEE 1988 Service Repair Manual
[x] Cancel search | Manufacturer: JEEP, Model Year: 1988, Model line: CHEROKEE, Model: JEEP CHEROKEE 1988Pages: 1378, PDF Size: 19.9 MB
Page 19 of 1378
emission control devices. This permits optimum engine performance
with minimum emissions.
OPERATION
The engine control system is divided into 6 sub-systems:
electronic control unit (also called the ECU or computer), sensors and\
switches, fuel control, emission control, idle speed control, and
ignition advance control.
ELECTRONIC CONTROL UNIT (ECU)
The ECU is located under the instrument panel, above the
accelerator pedal. It receives information from the 13 engine sensors
or switches to determine engine operating conditions at any particular
moment. The ECU responds to these signals by sending a control signal
to the fuel injector, fuel pump, ignition control module, idle speed
actuator (ISA) motor, EGR solenoid, and canister purge solenoid. It
also controls the Load Swap relay, and on Man. Trans. models, the up-
shift indicator lamp.
SENSORS & SWITCHES
Exhaust Gas Oxygen (EGO) Sensor
The amount of oxygen in exhaust gases varies according to the
air/fuel ratio of the intake charge. The exhaust gas oxygen sensor,
located in the exhaust pipe, detects this content and transmits a low
voltage signal to the ECU.
The outer surface of the sensor is exposed to exhaust gases,
the inner surface to outside air. The difference in the amount of
oxygen contacting the inner and outer surfaces of the sensor creates a
pressure, which results in a small voltage signal. This signal, which
is a measure of the unburned oxygen in the exhaust gas, is transmitted
to the ECU.
If the amount of oxygen in the exhaust system is low (rich
mixture), the sensor voltage signal will be high. If the mixture is
lean, the oxygen sensor will generate a low voltage signal.
The sensor has a heating element that keeps the sensor at
proper operating temperature during all operating modes.
Manifold Air/Fuel Temperature (MAT) Sensor
The manifold air/fuel temperature sensor is installed in the
intake manifold. This sensor provides a voltage signal to the ECU
representing the temperature of the air/fuel mixture in the intake
manifold. The ECU compensates for air density changes during high
temperature operation.
Coolant Temperature Sensor (CTS)
The coolant temperature sensor is located in the intake
manifold coolant jacket. This sensor provides a voltage signal to the
ECU. The ECU uses this signal to determine engine temperature. During
cold engine operation, the ECU responds by enriching the air/fuel
mixture delivered to the injector, compensating for fuel condensation
in the intake manifold, controlling engine warm-up speed, increasing
ignition advance, and inhibiting operation of the EGR system.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor detects absolute pressure in the intake
manifold as well as ambient atmospheric pressure. This information is
supplied to the ECU, through voltage signals, as an indication of
engine load. The sensor is attached to the plenum chamber near the
hood latch. A vacuum line from the throttle body supplies the sensor
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Manifold Absolute Pressure (MAP) Sensor
The MAP sensor measures changes in intake manifold pressure
resulting from engine load and speed changes. The MAP sensor is
located in the engine compartment, on the firewall behind the engine.
The ECU uses this information to control fuel delivery and ignition
timing.
Oxygen (O2) Sensor
The oxygen sensor is mounted in the exhaust manifold to
monitor oxygen content of exhaust gases. The oxygen content reacts
with the oxygen sensor to produce a voltage output signal which is
sent to the ECU.
The oxygen sensor is equipped with a heating element that
keeps the sensor at a consistent temperature under warm-up and idle
conditions. This allows the engine control system to enter "closed
loop" mode of operation much earlier, and to remain in "closed loop"
during extended idle periods.
The heating element of the sensor is controlled by the ECU
through the O2 sensor heater relay. This is a normally closed relay
that supplies voltage to the sensor under warm-up and idle conditions.
When the ECU receives information from the MAP and speed sensors
indicating that the sensor will stay heated due to exhaust gas
temperature, the ECU opens the relay to stop voltage to the heating
element.
Fig. 1: Location & Identification of 4.0L Relays
Throttle Position Sensor (TPS)
The TPS is a variable resistor connected to the throttle
shaft. The sensor is a potentiometer that has one end connected to the
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Fig. 4: MAP Sensor Terminal Identification
Oxygen Sensor
Oxygen sensor must be tested with System Tester (M.S. 1700).
Oxygen Sensor Heating Element
Disconnect electrical connector from oxygen sensor. Using an
ohmmeter, measure resistance between connector terminals "A" and "B"
(marked on connector). See Fig. 5. If resistance is not 5-7 ohms,
replace sensor.
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Fig. 5: Testing Oxygen Sensor Heating
Element Resistance
Knock Sensor
Knock sensor must be tested with System Tester (M.S. 1700).
Speed Sensor
Disconnect speed sensor electrical connector from the sensor.
Using an ohmmeter, measure resistance between connector terminals "A"
and "B" (marked on connector). If reading is not 125-275 ohms with
engine at normal operating temperature, replace speed sensor.
"Synch Pulse" (Stator)
1) Using an analog voltmeter, insert positive probe into Blue
wire at distributor connector. Insert negative probe into Gray wire
with tracer at distributor connector.
NOTE: Do not remove connector from distributor. Insert voltmeter
leads from rear of connector. Do not puncture wire.
2) With voltmeter set on "15-Volt A/C" scale, turn ignition
on. Voltmeter should indicate 5 volts. If voltage is indicated, go to
step 4). If no voltage is indicated, check voltmeter leads for good
connection and go to next step.
3) If there is still no voltage reading, turn ignition off
and remove ECU. Reconnect harness and turn ignition off and remove
ECU. Reconnect harness and turn ignition on. Check for voltage between
ECU pin "C-16" and good ground. If voltage still does not register,
test system with System Tester (M.S. 1700).
4) If 5 volts was detected, check for continuity at the
following points:
* Between Blue wire at distributor connector and terminal "C-16"
at ECU.
* Between Gray wire with tracer at distributor connector and
terminal "C-5" at ECU.
* Between Black wire at distributor connector and good ground.
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GND or GRND Ground
GRN Green
GRY Gray
Ga. Gauge
Gals. gallons
Gov. Governor
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"H" ABBREVIATION TABLE
"H" ABBREVIATION TABLE \
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ABBREVIATION DEFINITION
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H/D Heavy Duty
HAC High Altitude Compensation
HC Hydrocarbons
HEDF High Speed Electro Drive Fan relay or circuit
HEGO Heated Exhaust Gas Oxygen Sensor
HEGOG HEGO Ground circuit
HEI High Energy Ignition
HLDT Headlight
HO High Output
HP High Performance
HSC High Swirl Combustion
HSO High Specific Output
HTR Heater
HVAC Heating
Headlt. Headlight
Hg Mercury
Hgt. Height
Htr. Heater
Hz Hertz (Cycles Per Second)
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"I" ABBREVIATION TABLE
"I" ABBREVIATION TABLE \
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ABBREVIATION DEFINITION
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I.D. Inside Diameter
IAC Idle Air Control
IACV Idle Air Control Valve
IC Integrated Circuit
ID Identification
IDM Ignition Diagnostic Monitor
IGN Ignition system or circuit
ILC Idle Load Compensator
In. Hg Inches of Mercury
INCH Lbs. Inch Pounds
INFL REST Inflatable Restraint
INJ Injector or Injection
IP Instrument Panel
IPC Instrument Panel Cluster
ISA Idle Speed Actuator
ISC Idle Speed Control
ISS Idle Stop Solenoid
ITS Idle Tracking Switch
IVSV Idle Vacuum Switching Valve
Page 104 of 1378
\003
A/C -H EA TE R S YSTE M - M AN UAL
1988 J e ep C hero ke e
1988 Manual A/C-Heater Systems
JEEP
* PLEASE READ THIS FIRST *
CAUTION: When discharging air conditioning system, use only approved
refrigerant recovery/recycling equipment. Make every attempt
to avoid discharging refrigerant into the atmosphere.
DESCRIPTION
On Cherokee, Comanche and Wagoneer, the Climate Control
System is an integral assembly combining air conditioning, heating and
ventilating capabilities for models with air conditioning. The A/C
registers are built into instrument panel.
On Wrangler models, a dual flow unit with the capability of
recirculating air or drawing air from outside is used. It incorporates
under-dash registers and uses a blend-air type system.
The A/C components include a compressor, condenser, receiver-
drier, a sight glass (in the receiver-to-evaporator line) and
evaporator housing. Evaporator housing contains evaporator core,
expansion valve, thermostat, wiring and drain tube. Blower motor and
fan are located in blower housing, which is attached to evaporator
housing.
Vents provided in evaporator housing are adjustable to direct
air to different positions in vehicle's interior. System controls
include fan and temperature control knobs built into lower evaporator
housing assembly or temperature and mode levers on control panel
integrated with instrument panel.
OPERATION
A/C SYSTEM CONTROLS
Temperature & Fan Control Knobs
(Wrangler)
The right rotary control knob allows selection of desired
temperature. Knob has "OFF" "1", "2" and "3" positions for different
levels of cooling. The left rotary fan switch (knob) controls blower
motor speed. Knob has "OFF", "LOW", "MED" and "HI" positions. Fan will
operate unless mode control lever is in "OFF" position.
The A/C fan switch is a 3-speed unit used in conjunction with
a blower motor resistor. Fan switch controls low, medium and high
speed operation. Switch may be serviced by removing access plate
located on lower evaporator core housing, below control panel.
The A/C temperature control switch has a thermostat unit
built-in. Cooling adjustment is done by turning knob in a clockwise
rotation. For fast, efficient system operation in hot weather, vehicle
should be purged of hot air by driving about 2-3 city blocks with at
least one window open. During this time, temperature control knob
should be rotated clockwise to "MAX" position and fan control knob
placed in "HI" position. This allows evaporator to pre-cool and avoid
typical first blast of warm air.
Temperature Control Panel
(Cherokee, Comanche & Wagoneer)
The upper temperature control (mode) lever includes "MAX",
"NORM", "BI-LEVEL", "VENT", "HEAT" and "OFF" positions. At the far end
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* A /C -H EA TE R S YSTE M U NIF O RM IN SPEC TIO N G UID ELIN ES *
1 988 J e ep C hero ke e
GENERAL INFORMATION
A/C-Heater System Motorist Assurance Program
Standards For Automotive Repair
All Makes and Models
INTRODUCTION TO MOTORIST ASSURANCE PROGRAM (MAP)
CONTENTS
Motorist Assurance Program (MAP)
OVERVIEW
OVERVIEW OF SERVICE REQUIREMENTS & SUGGESTIONS
Heating, Ventilation and Air Conditioning
ACCUMULATORS
ACTUATORS (ELECTRICAL)
ACTUATORS (VACUUM)
AIR CONDITIONING FITTINGS
AIR CONDITIONING HOSES
AIR CONDITIONING METAL LINES, HOSES AND FITTING ASSEMBLIES
AIR CONTROL DOORS
AIR DAMS (EXTERNAL)
AIR DISTRIBUTION SYSTEM
BELTS
BLEND DOORS
BLOWER FANS (BLOWER WHEEL OR SQUIRREL CAGE)
BLOWER MOTORS
BLOWER RESISTORS
BLOWER SWITCHES
CABIN AIR FILTERS
CIRCUIT BREAKERS
COMPRESSOR CLUTCH ASSEMBLIES
COMPRESSORS
CONDENSER AIR SEALS
CONDENSER FAN MOTORS
CONDENSERS
CONNECTORS
CONTROL CABLES
CONTROL HEADS (FUNCTION SELECTORS)
CONTROL LINKAGES
CONTROL MODULES
COOLANT
COOLING FAN BLADES
COOLING FAN CLUTCHES
COOLING FAN MOTORS
EVAPORATOR DRAIN TUBES
EVAPORATOR PRESSURE REGULATORS (EPRS)
EVAPORATORS
EXPANSION VALVES
FUNCTION SELECTORS
FUSES, FUSIBLE LINKS AND CIRCUIT BREAKERS
FUSIBLE LINKS
GASKETS
HEATER CASES
HEATER CONTROL VALVES
HEATER CORES
Page 119 of 1378
are continually republished. In addition to these, standards for Drive
Train and Transmissions have recently been promulgated. Participating
shops utilize these Uniform Inspection & Communication Standards as
part of the inspection process and for communicating their findings to
their customers.
The Motorist Assurance Program continues to work
cooperatively and proactively with government agencies and consumer
groups toward solutions that both benefit the customer and are
mutually acceptable to both regulators and industry. We maintain the
belief that industry must retain control over how we conduct our
business, and we must be viewed as part of the solution and not part
of the problem. Meetings with state and other government officials
(and their representatives), concerned with auto repair and/or
consumer protection, are conducted. Feedback from these sessions is
brought back to the association, and the program adjusted as needed.
To assure auto repair customers recourse if they were not
satisfied with a repair transaction, the Motorist Assurance Program
offers mediation and arbitration through MAP/BBB-CARE and other non-
profit organizations. MAP conducted pilot programs in twelve states
before announcing the program nationally in October, 1998. During the
pilots, participating repair shops demonstrated their adherence to the
Pledge and Standards and agreed to follow the UICS in communicating
the results of their inspection to their customers. To put some
"teeth" in the program, an accreditation requirement for shops was
initiated. The requirements are stringent, and a self-policing method
has been incorporated which includes the "mystery shopping" of
outlets.
We welcome you to join us as we continue our outreach... with
your support, both the automotive repair industry and your customers
will reap the benefits. Please visit MAP at our Internet site www.
motorist.org or contact us at:
1444 I Street, NW Suite 700
Washington, DC 20005
Phone (202) 712-9042 Fax (202) 216-9646
January 1999
MAP UNIFORM INSPECTION GENERAL GUIDELINES
OVERVIEW OF SERVICE REQUIREMENTS & SUGGESTIONS
It is MAP policy that all exhaust, brake, steering,
suspension, wheel alignment, drive-line, engine performance and
maintenance, and heating, ventilation and air conditioning, and
electrical services be offered and performed under the standards and
procedures specified in these sections.
Before any service is performed on a vehicle, an inspection
of the appropriate system must be performed. The results of this
inspection must be explained to the customer and documented on an
inspection form. The condition of the vehicle and its components will
indicate what services/part replacements may be "Required" or
"Suggested". In addition, suggestions may be made to satisfy the
requests expressed by the customer.
When a component is suggested or required to be repaired or
replaced, the decision to repair or replace must be made in the
customer's best interest, and at his or her choice given the options
available.
This section lists the various parts and conditions that
indicate a required or suggested service or part replacement.
Although this list is extensive, it is not fully inclusive. In
addition to this list, a technician may make a suggestion. However,
any suggestions must be based on substantial and informed experience,
Page 121 of 1378
service to the system in question, if the repair creates
or continues an unsafe condition.
Reasons to Suggest Repair or Replacement
1 - Part is close to the end of its useful life (just above
discard specifications, or weak; failure likely to occur
soon, etc.)
2 - To address a customer need, convenience, or request (to
stiffen ride, enhance performance, eliminate noise,
etc.)
3 - To comply with maintenance recommended by the vehicle's
Original Equipment Manufacturer (OEM)
4 - Technician's recommendation based on substantial and
informed experience
NOTE: Suggested services are always optional. When presenting
suggested repairs to the customer, you must present the
facts, allowing the customer to draw their own conclusions
and make an informed decision about how to proceed.
HEATING, VENTILATION, AND AIR CONDITIONING
SERVICE PROCEDURES REQUIRED AND SUGGESTED FOR PROPER VEHICLE
OPERATION
CAUTION: Before working on any air conditioning system, be sure
to review current local, state, federal, and EPA
regulations regarding charging, recycling, and disposal
of refrigerant.
ACCUMULATORS
ACCUMULATOR INSPECTION \
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Condition Code Procedure
Attaching hardware
broken ................. A ... Require repair or replacement
of hardware.
Attaching hardware
missing ................ C .......... Require replacement of
hardware.
Attaching hardware not
functioning ............ A ... Require repair or replacement
of hardware.
Beyond vehicle
manufacturer's service
interval ............... 3 ............ Suggest replacement.
Dessicant at the end of
its useful life (saturated
with moisture) ......... 1 .. Suggest repair or replacement.
Dessicant bag
deteriorated ........... A ........ ( 1) Require replacement.
Further inspection required.
Leaking ................. A .. Require repair or replacement.
Threads damaged ......... A .. Require repair or replacement.
Threads stripped (threads
missing) ............... A ............ Require replacement.
Tubing connection
leaking ................ A .. Require repair or replacement.
Page 128 of 1378
Connector missing ....... C ............ Require replacement.
Inoperative ............. A ........ (2) Require replacement.
Insulation overheated ... A ............ Require replacement.
Terminal broken ......... A .. Require repair or replacement.
Terminal burned, affecting
performance ............ A ........... ( 1) Require repair or
replacement.
Terminal burned, not
affecting performance .. 2 .. Suggest repair or replacement.
Terminal corroded,
affecting performance .. A .. Require repair or replacement.
Terminal corroded, not
affecting performance .. 2 .. Suggest repair or replacement.
Terminal loose, affecting
performance ............ B .. Require repair or replacement.
Terminal loose, not
affecting performance .. 1 .. Suggest repair or replacement.
( 1) - Determine cause and correct prior to repair or
replacement of part.
( 2) - Inoperative includes intermittent operation or out of
OEM specification.
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BLOWER SWITCHES
See SWITCHES.
CABIN AIR FILTERS
CABIN AIR FILTER INSPECTION \
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Condition Code Procedure
Air flow obstruction .... A ............. Require cleaning or
replacement.
Maintenance intervals ... 3 ............ Suggest replacement.
Missing ................. C ............ Require replacement.
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CIRCUIT BREAKERS
See FUSES, FUSIBLE LINKS AND CIRCUIT BREAKERS .
COMPRESSOR CLUTCH ASSEMBLIES
COMPRESSOR CLUTCH ASSEMBLY INSPECTION \
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Condition Code Procedure
Air gap incorrect ....... B .. Require repair or replacement.
Bearing seized .......... A .. Require replacement of bearing
or assembly.
Bearing worn, affecting
performance ............ A .. Require replacement of bearing
or assembly.
Coil shows signs of
overheating ............ 1 .... Suggest replacement of coil.
Connector broken ........ A .. Require repair or replacement.
Connector (Weatherpack
type) leaking .......... A .. Require repair or replacement.
Connector melted,