check engine LEXUS SC400 1991 Service Owner's Manual

Check voltage between terminals MGC of air conditioner control assem-
bly connector and body ground.
(1) Remove console upper panel.(See page BO-111 ).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Start the engine.
Check voltage between terminals MGC of air condi-
tioner control assembly connector and body ground
when magnetic clutch is on and off by A/C
switch.
Go to step (7).
Check voltage between terminals MGC of air conditioner control assem-
bly harness side connector and body ground.
(1) Disconnect air conditioner control assemblyconnector.
(3) Turn ignition switch ON.
Check voltage between terminals MGC of air condi-
tioner control assembly harness side connector and
body ground.
Voltage: 4 ± 6 V
Check and replace air conditioner control
assembly.
Check for open and short in harness and connector between
air conditioner control assembly and engine & ECT ECU (See page IN-27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
±
AIR CONDITIONING SYSTEM TroubleshootingAC±87
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Check magnetic clutch relay.
Remove magnetic clutch relay from R/B No. 2
Check continuity between each pair of terminals
shown below of magnetic clutch relay.
(1) Apply battery voltage between terminals 2 and 3
(2) Check continuity between terminals 4 and 1
Replace magnetic relay.
(1) Remove engine & ECT ECU with connectors still connected.
(2) Turn ignition switch ON.
(1) Push one of the fan speed control switches
(Lo, Med or Hi).
(2) Measure voltage between terminal ACMG of engine & ECT ECU connector and body
ground.
Go to step (10).
Check voltage between terminal ACMG of engine & ECT ECU and
body ground.
Check for open and short in harness and connector between engine &
ECT ECU and battery (See page IN-27).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
Check for open and short in harness and connector between air conditioner control
assembly and compressor relay, compressor relay and battery (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control a ssembly.
AC±88±
AIR CONDITIONING SYSTEM Troubleshooting
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Water Valve VSV Circuit
CIRCUIT DESCRIPTION
If the target air mix damper position is on the hot side beyond a predeter\
mined level, the A/C control
assembly turns ON Tr inside the A/C control assembly.
This turns the water valve VSV ON so that engine coolant flows to the he\
ater core.
If the target air mix damper position is on the cool side beyond a prede\
termined level, the A/C control
assembly OFF Tr inside the A/C control assembly.
This turns OFF the VSV and stops circulation of engine coolant to the he\
ater core, thus increasing the
cooling performance.
DIAGNOSTIC CHART
Check voltage between terminal WV of A/C
control assembly connector and body
ground .
Check water valve VSV.
Check for open and short in harness
and connector between VSV and A/C
control assembly .
Check and replace A/C control assembly.
Replace water valve VSV.
Repair or replace harness or
connector.
Proceed to next circuit inspection
shown on matrix chart
(See page
AC-36).
WIRING DIAGRAM
AC±90±
AIR CONDITIONING SYSTEM Troubleshooting
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Check voltage between terminal WV of A/C control assembly connec-
tor body ground.
(1) Remove console upper panel.(See page
BO-111).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Start the engine.
Measure voltage between terminals WV of A/C con-
trol assembly connector and body ground
when the set temp. is not set to MAX COLD and
MAX HOT.
Proceed to next circuit inspection shown on
matrix chart. ( See page AC-36).
Check water valve VSV.
Water valve VSV connector.
Measure resistance between terminals of VSV con-
nector.
Resistance: 37 ± 47
at 20°C (68°F)
Check operation of water valve VSV when battery
voltage is applied to terminals of VSV connector or
not.

Battery voltage is applied:
The air from A is flowing out through B.

Battery voltage is not applied:
The air from A is flowing out through air filter.
Replace water valve VSV.
Check for open and short in harness and connector between VSV
and A/C control assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace A/C control assembly.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±91
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REFRIGERANT VOLUME
INSPECTION OF REFRIGERANT
VOLUME
1. RUN ENGINE AT IDLE SPEED
2. OPERATE A/C AT MAXIMUM COOLING FOR A FEWMINUTES
3. INSPECT AMOUNT OF REFRIGERANT Observe the sight glass on the liquid tube.
ItemSymptomAmount of refrigerantRemedy
1
Bubbles present in sight glassInsufficient*(1) Check for gas leakage with
gas leak tester and repair
if necessary
(2) Add refrigerant until bubbles disappear
2No bubbles present in sight
glassNone, sufficient or too muchRefer to items 3 and 4
3
No temperature difference
between compressor inlet and
outletEmpty or nearly empty(1) Check for gas leakage withgas leak tester and repair
if necessary
(2) Add refrigerant until bubbles disappear
4
Temperature between
compressor inlet and outlet is
noticeably differentProper or too muchRefer to items 5 and 6
5
Immediately after air conditioner
is turned off, refrigerant in sight
glass stays clearToo much(1) Recover refrigerant
(2) Evacuate air and charge
proper amount of
purified refrigerant
6
When air conditioner is turned
off, refrigerant foams and then
stay clearProper
±
*: Bubbles in the sight glass with ambient temperatures higher can be cons\
idered normal if cooling is sufficient.
REFRIGERANT CHARGE VOLUME
Specified amount: 950 + 50 g (33.44 + 1.76 oz)
±
AIR CONDITIONING SYSTEM Refrigerant VolumeAC±103
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DRIVE BELT TENSION
INSPECTION OF DRIVE BELT TENSION
1. INSPECT DRIVE BELT'S INSTALLATION CONDITIONCheck that the drive belt fits properly in the ribbed grooves.
2. INSPECT DRIVE BELT TENSION Check that the tension is within the A range on the auto ten-
sioner scale.
If the tension is not within the A range on the scale, replace
the belt with a new one.
HINT: When replacing the drive belt with a new one, the belt's
tension should be within the B range on the belt tensioner
scale.
IDLE±UP SPEED
INSPECTION OF IDLE SPEED
1. WARM UP ENGINE
2. INSPECT IDLE SPEED
 

Trans±
mission 

Magnetic clutch
condition 

Standard idle
speed (rpm)
 

A/T
(N range) 

No engaged
 

650 rpm
 


 

Engaged 

800 rpm
 M/T No engaged 700 rpm
  Engaged 900 rpm
AC±104±
AIR CONDITIONING SYSTEM Driver Belt Tension, Idle-Up Speed
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9. INSTALL EVAPORATORSee page AC±124
10. INSTALL INSTRUMENT PANEL REINFORCEMENT
11. INSTALL ENGINE See page EM±167
12. E V ACUATE AIR IN REFRIGERATION SYSTEM AND
CHARGE WITH REFRIGERANT
See page AC±17
Specified amount: 950 + 50 g (33.44 + 1.76 oz)
13. INSPECT FOR LEAKAGE OF REFRIGERANT
Using a gas leak tester, check for leakage of refrigerant.
±
AIR CONDITIONING SYSTEM TroubleshootingAC±109
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COMPRESSOR
INSPECTION OF COMPRESSOR
(Magnetic Clutch)
See page AC±86
(Compressor)
1. INSTALL MANIFOLD GAUGE SET
See page AC±15
2. START ENGINE
3. INSPECT COMPRESSOR FOR METALLIC SOUND Check that there is metallic sound from the compressor when
the A/C switch is turned on.
If a metallic sound is heard, replace the compressor assem-
bly.
4. INSPECT PRESSURE OF REFRIGERATION SYSTEM See ºInspection of Refrigeration System with Manifold
Gauge Setº on page.
5. STOP ENGINE
6. INSPECT VISUALLY FOR LEAKAGE OF REFRIGERANT FROM SAFETY SEAL
If there is any leakage, replace the compressor assembly.
AC±110
±
AIR CONDITIONING SYSTEM Troubleshooting
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EXPANSION VALVE
ON±VEHICLE INSPECTION
1. CHECK QUANTITY OF GAS DURING REFRIGERATIONCYCLE
2. INSTALL MANIFOLD GAUGE SET
3. RUN ENGINE
Run the engine at 2,000 rpm for at least 5 minutes. Then
check that the high pressure reading is 1,275±1,471 kPa
(13±15 kgf/cm, 185±213 psi).
4. CHECK EXPANSION VALVE If the expansion valve is faulty, the low pressure reading will
drop to 0 kPa (0 kgf/cm, 0 psi), otherwise it is OK.
HINT: When the low pressure drops to 0 kPa (0 kgf/cm, 0 psi),
feel the receiver's IN and OUT sides for no temperature differ-
ence.
REMOVAL OF EXPANSION VALVE
1. REMOVE EVAPORATOR See page AC±124.
2. REMOVE EQUALIZER TUBES
3. REMOVE EXPANSION VALVE
INSTALLATION OF EXPANSION VALVE
1. INSTALL EXPANSION VALVE
Specified torque:
0.31 inch tube 13 N Vm (135 kgf Vcm, 10 ft Vlbf)
0.50 inch tube 22 N Vm (225 kgf Vcm, 16 ft Vlbf)
2. INSTALL EQUALIZER TUBES
3. INSTALL EVAPORATOR
See page AC±124
AC±126
±
AIR CONDITIONING SYSTEM Expansion Valve
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(1) Turn ignition switch LOCK.
(2) Disconnect center airbag sensor assemblyconnector.
(3) Turn ignition switch ON. But do not start engine.
(4) Measure voltage at IG
2 or ACC on connector
wire harness side of center airbag assembly and
operate electric system (defogger, wiper,
headlight, heater, blower, etc.).
Voltage: 6 V ± 11.5 V at IG
2 and ACC.
(5) Turn electric system switch OFF.
(6) Turn ignition switch LOCK.
(7) Remove voltmeter and connect center airbag sensor assembly.
Does airbag warning light turn off after approx. 10 seconds?
Preparation.
Turn ignition switch ON.
Operate electric system checked in [ 1 ] (4) and
check that airbag warning light goes off after
approx. 10 seconds.
Check diagnostic code, and if a malfunction
code is output, perform troubleshooting
according to malfunction code. If a normal
code is output, replace center airbag
sensor assembly.
Check battery and charging system
(See page CH±1)
INSPECTION PROCEDURE
AB±41SRS AIRBAG ± Troubleshooting
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