battery LEXUS SC400 1991 Service User Guide

Check voltage between terminals B of air conditioner control assembly
connector and body ground.
(1) Remove console upper panel.(See page BO-111 ).
(2) Remove A/C control assembly with connec±
tors still connected.
Measure voltage between terminals B of air condi-
tioner control assembly connector and body
ground.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix
chart (See page AC-36).
Check DOME fuse.
Remove DOME fuse from R/B No. 2.
Check continuity of DOME fuse.
Continuity.
Check for short in all the harness and
components connected to the DOME fuse
(See attached wiring diagram).
Check and repair harness and connector between air conditioner control \
assembly and battery.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±75
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Heater Main Relay Circuit
CIRCUIT DESCRIPTION
The heater main relay is switched on by signals from the air conditioner co\
ntrol assembly.
It supplies power to the blower motor.
DIAGNOSTIC CHART
Check voltage between terminals HR of air
conditioner control assembly connector
and body ground.
Check heater main relay.
Check HTR fuse.
Check and repair harness and connector
between air conditioner control assembly
and battery.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36
).
Check for short in all the harness
and components connected to
the HTR fuse (See
attached wiring diagram).
Replace heater main relay.
WIRING DIAGRAM
AC±76±
AIR CONDITIONING SYSTEM Troubleshooting
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Check voltage between terminals HR 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.
Proceed to next circuit inspection shown on ma-
trix chart (See page AC-36).
Check heater main relay.
Check continuity between each pair of terminals of
heater main relay shown below.
Measure voltage between terminals HR of air condi-
tioner control assembly and body ground when
ignition switch is on and off.
(1) Apply battery voltage between terminals 1
and 3
(2) Check continuity between each pair of ter±minal shown below.
Replace heater main relay.
Remove HTR fuse from J/B No. 1.
Check continuity of HTR fuse
Continuity
Check for short in all the harness and
components connected to the HTR fuse
See attached wiring diagram).
Check and repair harness and connector between air conditioner control \
assembly and battery.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±77
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Check power transistor.
(1) Remove cooling unit (See page BO-107).
(2) Disconnect power transistor connector.
(1) Check test bulb lights up when battery and
resistor are connected to power transistor
connector as left illustration shows.
(2) Measure resistance between terminal 2 and 3
(1) The bulb lights up.
(2)Resistance: 2.0± 2.4 k 
Replace power transistor.
Check for open and short in harness and connector between air
conditioner control assembly and power transistor (See page IN-27).
Repair or replace harness or connector.
Proceed to next circuit inspection shown on matrix
chart (See page AC-36).
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±79
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Blower Motor Circuit
CIRCUIT DESCRIPTION
This is the power source for the blower motor.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check blower motor.
Check harness and connector between battery
and blower motor, blower motor and body ground
(See page IN±37).
Check blower resistor.
Replace blower motor.Replace blower motor.
Replace blower resistor.
Repair or replace harness or
connector.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36).
AC±80±
AIR CONDITIONING SYSTEM Troubleshooting
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Check blower motor.
Remove blower motor.(See page AC-129).
Connect positive
lead connected to terminal 2 of
blower motor connector, negative  lead to
terminal 1.
Blower motor operates smoothly.
Replace blower motor.
Check blower resistor.
Disconnect blower resistor connector.
Measure resistance between terminals 1 and 2 of
blower resistor connector.
Resistance: 2.6 ± 3.0

Replace blower resistor.
Check for open short in harness and connector between battery
and blower motor, blower motor and body ground (See page IN-27)
Repair or replace harness or connector.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±81
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Check voltage between terminals A/C IN of air
conditioner control assembly connector and
body ground .
Check A/C compressor magnetic clutch.
Check harness and connector between
A/C compressor and compressor relay
(See page IN-27).
Proceed to next circuit inspection
shown on matrix chart (See page AC-36).
Check voltage between terminals MGC of air
conditioner control assembly connector and
body ground .
Check voltage between terminals MGC of air
conditioner control assembly harness side con-
nector and body ground .
Check harness and connector between
air conditioner control assembly and
engine & ECT ECU (See page iN±27).
Check and replace engine & ECT ECU.
Check magnetic clutch relay.
Repair A/C compressor magnetic
clutch.
Repair or replace harness or
connector.
Check and replace air conditioner
control assembly.
Repair or replace harness or
connector.
Replace magnetic clutch relay.
Check voltage between terminals ACMG of
engine & ECT ECU and body ground .
Check harness and connector between
engine & ECT ECU and battery (See page
IN-27).
Check and replace engine & ECT ECU.
Repair or replace harness or
connector.
Check 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
assembly.
±
AIR CONDITIONING SYSTEM TroubleshootingAC±85
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Check voltage between terminals A/C IN of air conditioner control
assembly connector and body ground.
(1) Remove console upper panel.(See pageBO-111 ).
(2) Remove A/C control assembly with
connectors still connected.
(3) Start the engine.
Check voltage between terminals A/C IN of air condi-
tioner control assembly and body ground when mag-
netic clutch is on and off by A/C switch
Go to step (4).
Check air conditioner compressor magnetic clutch.
Disconnect magnetic clutch connector.
Connect positive
lead connected to battery to mag-
netic clutch connector terminal 3.
Magnetic clutch is energized.
Repair air conditioner compr essor magnetic
clutch.
Check for open and short in harness and connecter between air
conditioner compressor and compressor relay (See page IN-27).
Repair or replace harness or connector.
Proceed to next circuit inspection shown on ma-
trix chart (See page AC-36).
INSPECTION PROCEDURE
AC±86±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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
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AIR CONDITIONING SYSTEM TroubleshootingAC±91
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