ignition switch LEXUS SC400 1991 Service User Guide

Check voltage between terminals TW and SG of air conditioner control
assembly connector.
(1) Remove console upper panel. (See page BO±111 )
(2) Remove A/C Control Assembly with connectors
still connected.
(3) Turn ignition switch ON.
Measure voltage between terminals TW and SG of air
conditioner control assembly connector at each tem-
perature.
Voltage
at 0°C (32°F) : 2.8~3.2 V
at 40°C (104°F) : 1.8~2.2 V
at 70°C (158°F) : 0.9~1.3 V
In addition, as the temperature increases, the
voltage decreases gradually.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).However,
when Diag. code 14 is displayed, check and
repair air conditioner control assembly.
Check water temperature sensor.
(1) Remove heater unit.
(2) Remove water temperature sensor.
Measure resistance between terminals 1 and 3 of
water temperature sensor connector at each temper-
ature.
Resistance
at 0°C (32°F) : 16.5~17.5 k

at 40°C (104°F) : 2.4~2.8 k

at 70°C (158°F) : 0.7~1.0 k

In addition, as the temperature increases, the
voltage decreases gradually.
Replace water temperature sensor.
Check for open and short in harness and connector between air conditioner
control assembly and water temperature sensor (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±51
WhereEverybodyKnowsYourName

99
Check voltage between terminals S5 and TS of air conditioner
control assembly connector.
(1) Remove console upper panel. (See page
BO-111 ).
(2) Remove A/C control assembly with connec-
tors still connected.
(3) Turn ignition switch ON.Measure voltage between terminals S5 and TS
of air conditioner control assembly connector
when the solar sensor is subjected to an electric
light, the sensor is covered by a cloth.
ConditionVoltage
Sensor subjected to electric light
Sensor covered by a cloth
Below 4 V
4 ±4.5 V
In addition, when the inspection light is gradu-
ally moved away from the sensor, the voltage
increases.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).However,
when Diag. code 21 is displayed, check and
replace air conditioner control assembly.
Check solar sensor.
(1) Remove solar sensor from dashboard.
(2) disconnect solar sensor connector.
Connect positive (+) lead of ohmmeter to terminal 2
and negative (±) lead to terminal 1 of the solar sensor.
(1) Cover the sensor by a cloth.
(2) Measure resistance between terminals 1 and 2 of solar sensor connector.
(1) Remove the cloth from the solar sensor andsubject the sensor to electric light.
(2) Measure resistance.
Resistance: Approx, 4 k
(continuity)
In addition, as the electric light is moved gradu-
ally away from the sensor the resistance in-
creases.
Replace solar sensor.
Check for open and short in harness and connector between air conditioner
control assembly and solar sensor (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±53
WhereEverybodyKnowsYourName

9
Check voltage between terminals LP of air conditioner control
assembly and body ground.
(1) Install the manifold gauge set.(See page AC-15).
(2) Turn ignition switch ON.
Check voltage between terminals LP of air conditioner
control assembly connector and body ground when the
air conditioner gas pressure is
changed.
The voltage changes with gas pressure, as shown
in the diagram below.
Low Pressure Cut Side
High pressure Cut Side
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).
Check pressure switch.
Disconnect pressure switch connector.
Check continuity between terminals 1 and 4 of pres-
sure switch when air conditioner gas pressure is
changed.
The continuity changes with gas pressure as
shown below.
Low Pressure Cut Side
High pressure Cut Side
Replace pressure switch
Check for open and short in harness and connector between air conditioner control
assembly and pressure switch, pressure switch and body ground (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±57
WhereEverybodyKnowsYourName

Check voltage between terminals TP and SG of air conditioner control
assembly connector.
(1) Remove console upper panel.(See page BO±111).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Change the set temperature to activate the air mix
damper, and measure the voltage between termi-
nals TP and SG of air conditioner control assem-
bly connector each time when the set temperature
is changed.
Set TemperatureVoltage
Max. cool
Max. hot 3.70± 4.27 V
0.88 ± 1.16 V
In addition, as the set temperature increases,
the voltage decreases gradually without inter-
ruption.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).However,
when Diag. code 31 or 41 is displayed, check and
replace air conditioner control assembly.
Check air mix damper position sensor.
(1) Remove heater unit. (See page AC-125)
(2) Disconnect air mix servomotor assembly
connector.
Measure resistance between terminals S5 and SG of
air mix servomotor assembly connector.
Resistance:4.7~7.2 k

While operating air mix servomotor as in the
procedure on page AC-61, measure resistance
between terminals TP and SG of air mix servo-
motor assembly connector.
Position Resistance
Max. cool
Max. warm 3.76 ~ 5.76 k


0.94 ~ 1.44 k

As the air mix servomotor moves from cool side
to warm side, the resistance decreases gradually
without interruption.
Replace air mix servomotor assembly.
Check for open and short in harness and connector between air conditioner
control assembly and air mix servomotor assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±59
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Check voltage between terminals TP1 and SG of air conditioner control
assembly connector.
(1) Remove console upper panel.(See page BO-111).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Press REC/FRS switch to change the air inlet
between fresh and recirculation air, and measure
voltage between terminals TP1 and SG of air
conditioner control assembly when the air inlet
servomotor operates.
In addition, as the air inlet servomotor is moved
from REC side to FRS side, the voltage de-
creases gradually without interruption.
Proceed to next circuit inspection shown on matrix chart
(See page AC-36).However, when Diag. code 32 or 42 is
displayed, check and replace air conditioner control assem-
bly.
Check air inlet damper position sensor.
(1) Remove heater unit. (See page AC-127)
(2) Disconnect air inlet servomotor assembly
connector.
Measure resistance between terminals S5 and SG of
air inlet servomotor assembly connector.
Resistance: 4.7~7.2 k

While operating air inlet servomotor as in the
procedure on page AC-65, measure resistance
between terminals TP1 and SG of air inlet servo-
motor assembly connector.
Resistance:
As the air inlet servomotor moves from REC side
to FRS side, the resistance decreases gradually
without interruption.
Replace air inlet servomotor assembly.
Check for open and short in harness and connector between air conditioner
control assembly and air inlet servomotor assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control assembly.
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM REPAIR INSTRUCTIONSAC±63
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Check voltage between terminals TPM and SG of air conditioner control
assembly connector.
(1) Remove console upper panel.(See page BO-111 ).
(2) Remove A/C control assembly with
connectors still connected.
(3) Turn ignition switch ON.
In addition, as the air outlet servomotor is moved
from REC side to FRS side, the voltage decreases
gradually without interruption.
Proceed to next circuit inspection shown on matrix chart
(See page AC-36).However, when Diag. code 32 or 42 is dis-
played, check and replace air conditioner control assembly.
Check air outlet damper position sensor.
(1) Remove heater unit. (See page AC-127)
(2) Disconnect air outlet servomotor assembly
connector.
Measure resistance between terminals S5 and SG of
air outlet servomotor assembly connector.
Resistance: 4.7~7.2 k

While operating air outlet servomotor as in the
procedure on page AC-69, measure resistance
between terminals TP1 and SG of air outlet servo-
motor assembly connector.
Resistance:
As the air inlet servomotor moves from DEF side
to FACE side, the resistance decreases gradually
without interruption.
Replace air outlet servomotor assembly.
Check for open and short in harness and connector between air conditioner
control assembly and air outlet servomotor assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control assembly.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±67
WhereEverybodyKnowsYourName

Check voltage between terminals IG+ and E of air conditioner control
assembly connector.
(1) Remove console upper panel.(See pageBO-111 ).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Measure voltage between terminals IG+ and E of air
conditioner control assembly.
Voltage: 10 ±14 V
Proceed to next circuit inspection shown on matrix
chart (See page AC-36).
Check continuity between terminals E of air conditioner control assem-
bly and body ground.
Measure resistance between terminals E of air condi-
tioner control assembly and body ground.
Resistance:1  or less
Repair or replace harness or connector.
Remove HTR fuse from J/B No. 1.
Check continuity of HTR fuse
Continuity
Check HTR fuse.
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±71
WhereEverybodyKnowsYourName

Check voltage between terminals ACC 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.
(3) Turn ignition switch ON.
Measure voltage between terminals ACC of air
conditioner control assembly connector and body
ground.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix
chart (See page AC-36).
Check RADIO No. 2 fuse.
Remove RADIO No. 2 fuse from J/B No. 1.
Check continuity of RADIO No. 2 fuse.
Continuity.
Check for short in all the harness and
components connected to the RADIO No. 2
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±73
WhereEverybodyKnowsYourName

\
\


\

\
\
Back±up Power Source Circuit
CIRCUIT DESCRIPTION
This is the backup power source for the air conditioner control assembly. Power is supplied even when
the ignition switch is off and is used for diagnostic code memory, etc.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check voltage between terminal B of air
conditioner control assembly connector
and body ground.
Check DOME fuse.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36
).
Check and repair harness and connector
between air conditioner control assembly
and battery.
Check for short all in the harness
and components connecteds to
the DOME fuse (See attached wiring
diagram)
AC±74±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

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
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AIR CONDITIONING SYSTEM TroubleshootingAC±77
WhereEverybodyKnowsYourName