1991 MITSUBISHI MONTERO ECU

HIGH PRESSURE SWITCH
The high pressure switch, installed in refrigerant line, is
wired in series with compressor clutch. When refrigerant pressures
rise above switch control pressure point, power to compressor clutch
is cut. The high pressure switch may also be activated when airflow
through condenser is blocked or when system is overcharged.
HIGH/LOW PRESSURE CUT-OFF SWITCH
The High/Low Pressure Cut-Off (HLPCO) switch, located on
refrigerant line, is wired in series with compressor clutch. Switch
cuts off power to compressor clutch when refrigerant pressures are
above or below switch control point. When pressure returns to normal
operating range, compressor clutch operation resumes.
LOW PRESSURE SWITCH
The low pressure switch, located in receiver-drier, is wired
in series with compressor clutch. When refrigerant pressure drops
below switch control point (usually due to leak in system), power to
compressor clutch is cut.
REFRIGERANT TEMPERATURE SWITCH
The refrigerant temperature switch, located on rear of
compressor, detects refrigerant temperature discharged from
compressor. A/C Control Unit (ACCU) uses this information to control
compressor clutch cycling.
ADJUSTMENTS
NOTE: For adjustment procedures not covered in this article, see
appropriate HEATER SYSTEM article in the AIR CONDITIONING &
HEAT Section.
MODE CONTROL CABLE
Montero
Move mode selector lever to far left (DEF) position. Move
mode door lever upward in direction indicated by arrow. See Fig. 2.
Connect inner wire to lever, and secure outer housing using clip.
Operate mode control knob to ensure proper operation.
Fig. 2: Adjusting Mode Selection Cable (Montero)
Courtesy of Mitsubishi Motor Sales of America.
TEMPERATURE CONTROL CABLE

Montero
1) Move temperature selector lever to far left position.
Remove heater control valve cover. Disconnect heater control valve
wire from blend door lever. Push heater control valve inward (closed).\
2) Move blend door lever downward in direction indicated by
arrow. See Fig. 3. Connect inner wire to lever, and secure outer
housing using clip. Adjust heater control valve wire so valve is fully
closed. Operate mode control knob to ensure proper operation.
Reinstall heater control valve cover.
Fig. 3: Adjusting Temperature Selection Cable (Montero)
Courtesy of Mitsubishi Motor Sales of America.
TROUBLE SHOOTING
AIR NOT COOL
1) Ensure compressor clutch is operating. If compressor
clutch is not operating, check fuses and relay. Check A/C switch.
Check high and low pressure switches or dual pressure switch. Check
thermistor, thermo relay or Electronic Cycling Clutch Switch (ECCS).

conductors exposed ..... A .. Require repair or replacement.
Insulation damaged,
conductors not exposed . 1 .. Suggest repair or replacement.
Missing ................. C ............ Require replacement.
Routed incorrectly ...... B ................. Require repair.
Secured incorrectly ..... B ................. Require repair.
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 replacement
of part.
( 2) - Inoperative includes intermittent operation.









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FUSIBLE LINKS
See FUSES, FUSIBLE LINKS AND CIRCUIT BREAKERS .
GASKETS
GASKET INSPECTION








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Condition Code Procedure
Leaking ................. A ........... ( 1) Require repair or
replacement.
( 1) - Require inspection of mating and sealing surface and
repair or replace as necessary.









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HEATER CASES
See PLENUMS.
HEATER CONTROL VALVES
HEATER CONTROL VALVE INSPECTION








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Condition Code Procedure
Application incorrect ... B ............ Require replacement.
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

specification .......... A .. Require repair or replacement.
Circuit shorted ......... A .. Require repair or replacement.
Connector melted,
affecting performance .. A ........... (1) Require repair or
replacement.
Connector melted, not
affecting performance .. 2 ........... ( 1) Suggest repair or
replacement.
Connector missing ....... C ............ Require replacement.
Diode open .............. A .. Require repair or replacement.
Diode shorted ........... A .. Require repair or replacement.
Insulation damaged,
conductors exposed ..... A .. Require repair or replacement.
Insulation damaged,
conductors not exposed . 1 ............ Suggest replacement.
Protective shield
(conduit) melted ....... B ........ ( 1) Require replacement.
Protective shield
(conduit) missing ...... C ............ Require replacement.
Routed incorrectly ...... B ................. Require repair.
Secured incorrectly ..... B ................. Require repair.
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.
Voltage drop out of
specification .......... A .. Require repair or replacement.
( 1) - Determine cause and correct prior to repair or
replacement of part.









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area. Always wear eye protection when working around air conditioning
systems and R-12. The system's high pressure can cause severe injury
to eyes and skin if a hose were to burst. R-12 evaporates quickly
when exposed to atmosphere, freezing anything it contacts.
2) Use care when handling refrigerant containers. DO NOT drop
or strike containers or expose refrigerant containers to excessive
heat. Containers must never be heated more than 125
F (52C). Never
expose R-12 directly to open flame.
CAUTION: When R-12 is exposed to an open flame, drawn into a running
engine, or detected with a Halide (propane) leak tester,
poisonous phosgene gas is formed. Keep work areas ventilated
and avoid running engines near work area.
USING INDIVIDUAL R-12 CANS
Disposable refrigerant cans (referred to as one pound cans)
have a flat type seal or a screw type seal, and proper can tap must be
used for each type. Be sure sealing gasket on can tap is in good
condition. A proper safety can tap will prevent refrigerant from
flowing back into open can, as tap has a one-way flow control.
NOTE: Recent findings by the EPA indicate that refrigerant is
harmful to the Earth's protective Ozone layer. When
discharging refrigerant avoid allowing refrigerant to enter
the atmosphere. Refrigerant recovery system should be used
when discharging the system.
MULTI-CAN DISPENSING VALVES
A multi-can dispensing valve allows attachment of several
cans of refrigerant, and is a good substitute when a bulk container is
not available. Cans are installed onto each leg of multi-can
dispensing valve in the same manner as the individual cans, and each
leg has its own can tap.
CAN TAP INSTALLATION FLAT TYPE SEAL CANS
On cam-lock or one-piece can taps, first turn the handle
outward to the fully open position. Securely engage locking lugs over
the can flange, and lock them in place by turning cam lock or locking
nut. Screw tap assembly into adapter so sealing gasket is fully seated
against the can top. Turn tap inward to pierce the can and close the
tap. DO NOT open tap until ready to purge the service hose or dispense
refrigerant into the system.
On 2-piece can taps, be certain tap handle is turned fully
inward to the closed position. Check that locking base is turned to
its outer limit. Securely engage locking lugs over the can flange.
Turn entire tap assembly (without disturbing the closed setting)
downward into the locking base to pierce the can. DO NOT open tap
until ready to dispense into system.
SCREW TYPE SEAL CANS
Ensure can tap is fully closed. Screw refrigerant can into
can tap fitting until tight. This will pierce the can. Connect tap to
center hose on manifold gauge set. DO NOT open tap until ready to
dispense R-12 into system.
WARNING: DO NOT open high side hand valve while air conditioning

system is in operation. This high pressure could rupture can
or fitting at safety can valve, resulting in damage and
personal injury.
CONNECTING LINES & FITTINGS
A new "O" ring should be used in all instances when
connecting lines and fittings (dip "O" ring in clean refrigeration oil
and make certain it is not twisted during installation). Always use
two wrenches to avoid twisting or distorting lines and fittings,
tighten coupling nuts securely.
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 a vacuum pump.
2) Charge the system with new R-12 (refrigerant) according t\
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each individual vehicle as outlined in the
GENERAL COOLING SYSTEM SERVICING article. Also see Refrigerant
Capacity in this Section.
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.
COMPRESSOR REMOVAL INFORMATION - ISOLATION METHOD
On systems which have compressors equipped with stem-type
service valves (Tecumseh), it is possible to isolate the compressor
for removal.
Isolating
Turn both high and low pressure manual valves to extreme
clockwise (front seat) position. Loosen cap on high pressure manual
valve connection to compressor and allow gas to escape until
compressor is relieved of pressure.
COMPRESSOR REMOVAL INFORMATION - DISCHARGE METHOD
This procedure is to be used on vehicles which have
compressor equipped with Schrader service valves. In these cases, the
compressor cannot be isolated and the system must be discharged, using
approved refrigerant recovery/recycling equipment, prior to compressor
removal.

NOTE: Idle mixture is computer controlled on fuel injected engines
and is nonadjustable. CO level specifications are not
available from manufacturer.
THROTTLE POSITION SENSOR (TPS)
TPS ADJUSTMENT
NOTE: Ensure basic idle speed is set to specification before
adjusting TPS. See BASIC IDLE SPEED under IDLE SPEED &
MIXTURE. Perform all adjustments with engine at normal
operating temperature, front wheels in straight-ahead
position, cooling fan and all accessories off, and
transmission in Park or Neutral.
TPS TEST APPLICATION









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Application Test
1.5L
Colt, Colt 200,
Mirage & Summit ............. TEST NO. 1
1.6L
Mirage ....................... TEST NO. 2
1.8L
Eclipse ...................... TEST NO. 3
2.0L (VIN V)
Colt Vista & Galant .......... TEST NO. 1
2.0L (VIN R & U)
Galant ....................... TEST NO. 1
Eclipse ...................... TEST NO. 3
2.4L
Pickup & Ram-50 .............. TEST NO. 1
3.0L
Montero, Pickup & Ram-50 ..... TEST NO. 4
Stealth & 3000GT ............. TEST NO. 5









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Test No. 1
1) Turn ignition on for more than 15 seconds. DO NOT start
engine. Turn ignition off. ISC plunger should be retracted fully.
2) Ensure ISC plunger is in fully retracted position.
Disconnect harness connector(s) from ISC motor. Turn ignition on. DO
NOT start engine.
3) Using digital voltmeter, backprobe terminal No. 19
(Green/White wire) and terminal No. 24 (Black or Green/Black wire) a\
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Engine Control Unit (ECU) wiring harness connector. Note TPS output
voltage.
4) If output voltage is .48-.52 volt, go to step 6). If
output voltage is not .48-.52 volt, loosen TPS mounting screw(s) and
rotate TPS clockwise, or counterclockwise, until output voltage is
within specification. Tighten TPS mounting screws.
5) Turn ignition off. Reconnect harness connector(s) at ISC
motor. Start engine. Ensure engine idles within curb idle speed
specification.
6) Turn ignition off. Disconnect negative battery cable for
at least 15 seconds to clear diagnostic trouble code. Reconnect
negative battery cable. Operate engine at idle for about 5 minutes to
ensure engine idles smoothly.
Test No. 2
1) Turn ignition on. DO NOT start engine. Loosen throttle

cable. Using digital voltmeter, backprobe terminal No. 19 (Green/White
wire) and terminal No. 24 (Black or Green/Black wire) at Engine
Control Unit (ECU) wiring harness connector. Check TPS output voltage.\
2) If output voltage is .48-.52 volt, go to step 3). If
output voltage is not .48-.52 volt, remove throttle body. Loosen TPS
mounting screws and rotate TPS clockwise, or counterclockwise, until
output voltage is within specification. Tighten TPS mounting screws.
3) Turn ignition off. Disconnect voltmeter from ECU harness
connector. Adjust throttle cable. Disconnect negative battery cable
for at least 10 seconds to clear diagnostic code. Reconnect negative
battery cable. Operate engine at idle for about 5 minutes to ensure
engine idles smoothly.
Test No. 3
1) Turn ignition on for more than 15 seconds. DO NOT start
engine. Turn ignition off. This should fully retract ISC plunger.
2) Ensure ISC plunger is fully retracted. Disconnect TPS
harness connectors. Connect Test Harness (MD998474) between
connectors. Connect digital voltmeter between Red and Blue wires of
test harness.
3) Turn ignition on. DO NOT start engine. TPS voltage should
be .48-.52 volt. If TPS voltage is .48-.52 volt, go to step 4). If TPS
voltage is not .48-.52 volt, loosen TPS mounting screws and rotate TPS
clockwise, or counterclockwise, until correct voltage is obtained.
Tighten TPS mounting screws.
4) Turn ignition off. Disconnect voltmeter and remove test
harness. Reconnect TPS harness connectors. Adjust throttle cable.
Start engine and check idle speed.
5) Turn ignition off. Disconnect negative battery cable for
at least 10 seconds to clear diagnostic trouble code. Reconnect
negative battery cable. Operate engine at idle for about 5 minutes to
ensure engine idles smoothly.
Test No. 4
1) Loosen throttle cable. Disconnect electrical connector
from TPS. Connect digital ohmmeter between Green/White and
Green/Yellow wire terminals of TPS electrical connector (on TPS side
of harness).
2) Insert .026" (.66 mm) feeler gauge between fixed Speed
Adjusting Screw (SAS) and throttle lever. See Fig. 4. Loosen TPS
mounting screws. Rotate TPS fully clockwise. Check for continuity
between Green/White wire and Green/Yellow wire terminals of TPS
electrical connector.
3) Rotate TPS counterclockwise until ohmmeter registers no
continuity. Tighten TPS mounting screws and reconnect TPS electrical
connector.
4) Using digital voltmeter, backprobe terminal No. 19
(Green/White wire) and terminal No. 24 (Black or Green/Black wire) a\
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Engine Control Unit (ECU) wiring harness connector. Turn ignition on.
DO NOT start engine. Check TPS output voltage.
5) If TPS output voltage is 0.4-1.0 volt, go to step 6). If
TPS output voltage is not 0.4-1.0 volt, check TPS and wiring harness
for damage or malfunction. Replace TPS or repair wiring harness if
necessary and go to next step.
6) Remove feeler gauge. Turn ignition off. Disconnect
voltmeter from ECU connector. Adjust throttle cable. Operate engine at
idle for about 5 minutes to ensure engine idles smoothly and within
specification.
Test No. 5
1) Disconnect electrical connector from TPS. Connect digital
ohmmeter between Yellow/Red wire and Black wire terminals of TPS.
2) Insert .026" (.66 mm) feeler gauge between fixed Speed