1988 JEEP CHEROKEE light

Isolating Compressor
1) Connect manifold gauge set to service valves on
compressor. Close both gauge valves. Open both service valves to the
mid-position.
2) Start engine and operate air conditioning. Turn suction
service valve slowly clockwise toward front-seated position. When
suction pressure is reduced to zero or less, stop engine and quickly
close suction service valve (front-seated).
3) Front-seat the discharge valve. Loosen oil check plug
slowly to release any internal pressure. Service valves can now be
removed from compressor and compressor removed from vehicle (if
necessary). Purge compressor after servicing.
Purging Compressor
1) Remove gauge set and place caps on service valve ports.
Back-seat the suction service valve to allow refrigerant to enter
compressor.
2) Loosen discharge port valve slightly. Loosen valve port
cap to allow refrigerant to force out air from compressor. Back-seat
the discharge valve and tighten the port cap. Compressor is ready for
service.
Compressor Oil Check
1) Operate system for 10 minutes, then stop and isolate
compressor. Loosen filler plug slowly to release any pressure in
crankcase.
2) Use dipstick to check oil level. See Fig. 2. Add oil as
necessary. Install plug with new "O" ring. Purge compressor of air.
Fig. 2: York Compressor Oil Level Dipstick
Check oil with shaft keyway facing head.
SYSTEM SERVICING CAUTIONS

Fig. 3: Assembling Ford Spring-Coupling Fitting
3) Lubricate both sides of fitting with clean refrigeration
oil. Assemble the fitting by pushing together with a slight twisting
motion. Check to make sure spring is over flared end of female
fitting.
PLACING SYSTEM IN OPERATION
After component replacement and/or system servicing has been
completed and all connections have been made, proceed as follows:
1) Evacuate the system using vacuum pump.
2) Charge the system with R-12. See REFRIGERANT CAPACITY in
the A/C SYSTEM SERVICE SPECIFICATIONS in this article.
3) Leak test the system, with particular attention to all new
connections and components.
4) Make a performance test of the system. Never assume that a
recharging has automatically corrected a problem.
DIAGNOSTIC PROCEDURES
Diagnosis is an important first step in A/C system servicing.
To save time and effort, systems should be carefully checked to
identify the causes of poor performance. By using the following
diagnostic charts, defective components or system damage can be
quickly located. To identify problems that are specific to one system,
refer to the repair sections of this article. The charts in this
article apply to all systems.
PREPARATION FOR TESTING
1) Attach Low and High side gauges.
2) Start engine and allow it to warm up.
3) Set system to COOL and blower to HIGH.
4) Open car doors and hood.
5) Run at fast idle for 2-3 minutes.

Tiny bubbles in sight
glass. Discharge air warm
when low side gauge drops
into vacuum.









\









\









\









\









\









\









\








Normal Normal Thermostatic switch system Defective Thermo-
only-compressor cycles off static Switch
and on too rapidly.









\









\









\









\









\









\









\








Normal Normal Cycling clutch systems Misadjusted Thermo
to High only-Compressor doesn't static Switch or
turn on soon enough. Defective Pressure
Discharge air becomes Sensing Switch
warm as low side
pressure rises.









\









\









\









\









\









\









\








Low Low Bubbles in sight glass. Low R-12 Charge
Outlet air slightly cool.









\









\









\









\









\









\









\








Low Low Sight glass clear or oil- Excessively Low
streaked. Outlet air very R-12 Charge
warm.









\









\









\









\









\









\









\








Low Low Outlet air slightly cool. Expansion Valve
Sweating or frost at Stuck Closed.
expansion valve. Screen Plugged or
Sensing Bulb
Malfunction









\









\









\









\









\









\









\








Low Low Outlet air slightly cool. Restriction on
High side line cool to High Side.
touch. Sweating or frost
on high side.









\









\









\









\









\









\









\








Low High Evaporator outlet pipe STV Stuck Open
cold. Low side goes into
vacuum when blower is
disconnected.









\









\









\









\









\









\









\








High Low Evaporator outlet pipe STV Stuck Open
warm. Outlet air warm.









\









\









\









\









\









\









\








High Low Noise from compressor Compressor
Malfunction









\









\









\









\









\









\









\








High High Outlet air warm. Condenser
Liquid line very hot. Malfunction or
Bubbles in sight glass. R-12 Overcharge









\









\









\









\









\









\









\








High High Outlet air slightly cool. Large Amount of
Bubbles in sight glass. Air and Moisture
in System.









\









\









\









\









\









\









\








High High Outlet air warm. Expansion Valve
Evaporator outlet Stuck Open.
sweating and frost.









\









\









\









\









\









\









\








(1) - If equipped with a low refrigerant charge protection system,
compressor operation may have stopped.









\









\









\









\









\









\









\








A/C SYSTEM SERVICE SPECIFICATIONS

reading and reverse leads. If readings are the same, replace diode
trio.
2) A good diode trio will give a high and low reading. Repeat
tests between single connector and each of the 3 connectors. Connect
ohmmeter to each of the 3 connectors. If any readings are zero,
replace diode trio.
NOTE: Before replacing diode trio, also check rectifier bridge.
DO NOT use high voltage, such as 110
volt test light, when
testing diode trio.
Fig. 4: Bench Testing Diode Trio
Rectifier Bridge Test
1) Position ohmmeter with one lead touching grounded heat
sink and the other lead touching flat metal on one of the 3 terminals

or threaded studs. Observe reading and reverse test lead connections.
See Fig. 5 .
2) If both readings are the same, replace rectifier bridge. A
good bridge will give a high and low reading. Retest all terminals (6
tests with insulated heat sink).
3) Connect test leads to insulated heat sink and one edge of
the 3 terminals. Observe reading and reverse connections. Repeat test
on all terminals (6 tests with insulated heat sink).
4) When all 12 tests have been made, testing is complete. DO
NOT use high voltage light to check bridge. DO NOT replace diode trio
or rectifier bridge unless at least one pair of readings is the same
(with leads reversed).
Fig. 5: Bench Testing Rectifier Bridge
OVERHAUL
NOTE: There are no overhaul procedures for CS130 alternators.
INSPECTION
Wash all metal parts except bearings, stator and rotor.
Inspect rotor slip rings. They may be cleaned with 400 grit or finer

how fast accelerator is depressed.
5) After throttle position is checked, technician will be
instructed to drive the vehicle. The DRB-II will indicate if a
requested action is seen by the TCM. If technician is requested to
perform a particular operation and TCM does not acknowledge the
action, press ENTER key to continue testing.
6) The TCM will instruct technician to accelerate vehicle at
light throttle to ensure transmission shifts through all gears,
indicating proper valve body solenoid operation.
7) During road test, ensure vehicle can be accelerated slowly
and evenly to allow transmission to enter all gear ranges without
downshifting or braking. If a failure is sensed, a diagnostic trouble
code will be displayed on DRB-II.
NOTE: If TCM senses a failure, control logic activates a specified
valve body solenoid to obtain a certain gear depending on
failure. Because transmission diagnostic trouble codes are
displayed one at a time, multiple diagnostic trouble codes
must be identified by retesting transmission.
STATE DISPLAY MODE
NOTE: STATE DISPLAY mode must be selected from AW4 MENU. See
ENTERING AW4 MENU under RETRIEVING DIAGNOSTIC TROUBLE CODES .
Select 3) STATE DISPLAY on DRB-II.
Module Information
When selecting module information option, the TCM version
will be indicated by a 2-digit number. Information can be used to
verify proper TCM application.
Sensor
1) When selecting sensor option, TPS and RPM indications will
be shown. The TPS indicator will display a 7 segment bar graph,
indicating TPS position and throttle plate angle.
2) A properly operating TPS should indicate 7 segments
through full throttle travel. The RPM indicator will display
transmission output shaft revolutions per minute.
Brake Switch Or Input/Output
Display indicates brake switch status, indicating whether
brake pedal is applied or released. Display also indicates shift lever
position, whether a valve body solenoid is on or off and present
transmission operating gear.
DRB-II PROBLEMS & ERROR MESSAGES
CARTRIDGE ERROR
1) If CARTRIDGE ERROR message is displayed, disconnect DRB-II
from transmission diagnostic connector. DO NOT touch keys on DRB-II
keypad. Reconnect DRB-II to transmission diagnostic connector and note
display.
2) If CARTRIDGE ERROR message is displayed, replace DRB-II
cartridge and proceed with diagnostics. If KEYPAD TEST FAILURE message
is displayed, replace DRB-II and proceed with diagnostics.
HIGH BATTERY
If HIGH BATTERY message is displayed, use external voltmeter
to check battery voltage at battery terminals. If battery voltage is
11.7-13.0 volts, replace DRB-II. If battery voltage is not 11.7-13.0

used with 2.5.L
The DRB-II has determined that the wrong Transmission Control
Unit (TCU) has been installed in the vehicle. There are two
transmission control units available for the Jeep AW4 transmission.
One is for the 4-cylinder 2.5L engine and the other is for the 6-
cylinder 4.0L engine.
1) using the DRB-II, read MODULE INFO. See HELP 1 for
assistance.
2) Determine what vehicle should be in the vehicle.
* 2.5L Engine: TCU 02 (Used in earlier years only)
* 4.0L Engine: TCU 01 (1993-94)
3) If the wrong transmission control unit is installed, the
vehicle shift points will be slightly different (the 2.5L engine TCU
has higher shift points).
TEST 10A - TESTING FOR INTERMITTENT SPEED SENSOR
NOTE: Perform TEST 1A - VERIFICATION OF THE COMPLAINT
before proceeding.
Fig. 115: Test 10A - Flow Chart (1 of 2)
Fig. 116: Test 10A - Schematic (Cherokee)

Installation
1) Install brake switch in retainer. Reconnect brake switch
electrical connector.
2) To check brake switch adjustment, slightly depress brake
pedal and note operation of brake switch plunger. Brake switch plunger
should fully extend when brake pedal free play is taken up and brake
application begins.
3) Clearance between brake switch plunger and brake pedal
should be approximately 1/8". If clearance is not within
specification, pull brake pedal rearward as far as possible.
4) Brake pedal should contact brake switch plunger, pushing
brake switch backward in retainer to provide proper adjustment. Ensure
brake lights operate.
5) Recheck clearance between brake switch plunger and brake
pedal with brake pedal depressed and free play taken up. Reinstall
lower steering column cover or trim panels.
NEUTRAL SAFETY SWITCH
NOTE: Neutral safety switch may be referred to as park/neutral or
gear select switch.
Removal
1) Apply parking brake. Raise and support vehicle. Disconnect
electrical connector at neutral safety switch. Pry lock washer tabs
away from retaining nut. See Fig. 126.
2) Remove retaining nut, lock washer and adjusting bolt. See
Fig. 126 . Remove neutral safety switch from manual valve shaft.
Installation
1) Disconnect shift control rod from transmission shift
lever. Rotate transmission shift lever fully rearward and then forward
2 detents to Neutral position.
2) Install neutral safety switch on manual valve shaft.
Install adjusting bolt but DO NOT tighten at this time.
3) Install lock washer and retaining nut. Tighten retaining
nut to specification. See TORQUE SPECIFICATIONS. DO NOT bend over lock
washer tabs at this time.
4) Ensure transmission is still in Neutral. Rotate neutral
safety switch and align neutral standard line with vertical groove on
manual valve shaft. See Fig. 126.
5) Tighten the adjusting bolt to specification. Refer to the
TORQUE SPECIFICATIONS table. Bend lock washer tabs over. Reconnect
shift control rod and electrical connector. Ensure vehicle starts in
Park and Neutral only.
Fig. 126: Installing Neutral Safety Switch
Courtesy of Chrysler Corp.
SPEED SENSOR