display LEXUS SC400 1991 Service User Guide

Check voltage between terminals TAM 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.
Check voltage between terminals TAM and SG of air
conditioner control assembly connector at each tem-
perature.
at 25°C (77°F) : 1.35~1.75 V
at 40°C (104°F) : 0.85~1.25 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 11 is displayed, check and
replace air conditioner control assembly.
Check ambient temperature sensor.
(1) Remove under cover
(2) disconnect ambient temperature sensor connector.
Check resistance between terminals 1 and 2 of
ambient temperature sensor connector at each
temperature.
Resistance
at 25°C (77°F) : 1.6~1.8k

at 50°C (122°F) : 0.5~0.7k

In addition, as the temperature increases, the
voltage decreases gradually.
Replace ambient temperature sensor.
Check for open and short in harness and connector between air conditioner
control assembly and ambient temperature sensor (See page IN-27).
Repair or replace harness or connector.
Check and repair air conditioner control
assembly.
Voltage
INSPECTION PROCEDURE
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AIR CONDITIONING SYSTEM TroubleshootingAC±47
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Diag. Code 13Evaporator Temperature Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the temperature inside the cooling unit and sends the ap\
propriate signals to the air
conditioner control assembly.
Code No.Diag. Code Detecting ConditionTrouble area
13
Open or short in evaporator temperature sensor
circuit.
Evaporator temperature sensor.

Harness or connector between evaporator
temperature sensor and A/C control
assembly.

A/C control assembly.
DIAGNOSTIC CHART
Check voltage between terminals TE
and SG of air conditioner control as-
sembly
Check evaporator temperature sensor.
Check harness and connector between air
conditioner control assembly and evapora-
tor temperature sensor (See page IN-27).
Check and replace air conditioner control
assembly. 10Proceed to next circuit inspection
shown on matrix chart (See page
AC-36
). However, when Diag. code
13 is displayed, check and replace
air conditioner control assembly.
Replace evaporator temperature
sensor.
Repair or replace harness or
connector.
AC±48±
AIR CONDITIONING SYSTEM Troubleshooting
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(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 TE and SG of air
conditioner control assembly connector at each tem-
perature.
Voltage
at 0°C (32°F) : 2.0~2.4 V
at 15°C (59°F) : 1.4~1.8 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 11 is displayed, check and
replace air conditioner control assembly.
Check voltage between terminals TE and SG of air conditioner control
assembly connector.
Check evaporator temperature sensor.
Remove evaporator temperature sensor(See page
AC-124 ).
Check resistance between terminals 1 and 2 of evap-
orator temperature sensor connector at each temper-
ature.
In addition, as the temperature increases, the
voltage decreases gradually.
Replace evaporator temperature sensor.
Check for open and short in harness and connector between air conditioner
control assembly and evaporator temperature sensor (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
Resistance
at 15°C (59°F) : 2.1~2.6k

at 0°C (32°F) : 4.6~5.1k

INSPECTION PROCEDURE
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Diag. Code 14Water Temperature Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the coolant temperature and sends the appropriate signal\
s to the air conditioner
control assembly. These signals are used for warm up control when the engine is cold.
Code No.Diag. Code Detecting ConditionTrouble area
14
Open or short in water temperature sensor
circuit.
Water temperature sensor.

Harness or connector between water
temperature sensor and A/C control as-
sembly.

A/C control assembly.
DIAGNOSTIC CHART
Check voltage between terminals TW and
SG air conditioner control assembly con-
nector.
Check water temperature sensor.
Check harness and connector between air
conditioner control assembly and water tem-
perature sensor.(See page IN-27).
Check and replace air conditioner control
assembly. Proceed to next circuit inspection
shown on matrix chart (See page
AC-36
). However, when Diag. code
14 is displayed, check and replace
air conditioner control assembly.
Replace water temperature
sensor.
Repair or replace harness or
connector.
AC±50±
AIR CONDITIONING SYSTEM Troubleshooting
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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
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Diag. Code 21Solar Sensor Circuit
CIRCUIT DESCRIPTION
A photo diode in the solar sensor detects solar
radiation and sends signals to the air conditioner
control assembly.
Code No.Diag. Code Detecting ConditionTrouble area
21
Open or short in solar sensor circuit. (Please
note that display of diagnostic code 21 is not
abnormal when the sensor is not receiving
solar radiation)
Solar sensor.

Harness or connector between solar sensor
and A/C control assembly.

A/C control assembly.
DIAGNOSTIC CHART
Check voltage between terminals S5
and TS of air conditioner control as-
sembly connector.
Check solar sensor.
Check harness and connector between air
conditioner control assembly and solar sen-
sor (See page IN-27).
Check and replace air conditioner control
assembly. 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.
Replace solar sensor.
Repair or replace harness or
connector.
AC±52±
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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
±
AIR CONDITIONING SYSTEM TroubleshootingAC±53
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Diag. Code 22Compressor Lock Sensor Circuit
CIRCUIT DESCRIPTION
This sensor sends 4 pulses per engine revolution to the air conditioner cont\
rol assembly.
If the number ratio of the compressor speed, divided by the engine speed i\
s smaller that a predetermined
value, the air conditioner control assembly turns the compressor off. And, the indicator flashes at about
1 second intervals.
Code No.Diag. Code Detecting ConditionTrouble area
22
All conditions below are detected for 3 secs.
or more. (a) Engine rpm: 450 rpm or more
(b) Ratio between engine and compressor
rpm deviates 20% or more in comparison to
normal operation.
Compressor

Compressor drive belt.

Compressor lock sensor.

Harness and connector between compressor
and A/C control assembly.

A/C control assembly.
DIAGNOSTIC CHART
Check compressor.
Check compressor lock sensor.
Check harness and connectors between air
conditioner control assembly and compres-
sor sensor (See page IN-27).
Proceed to next circuit inspection shown on
matrix chart (See page AC-36). However,
when Diag. code 22 is displayed, check
and replace air conditioner control assem-
bly.
Adjust drive belt tension or repair
compressor.
Replace compressor lock sensor.
Repair or replace harness or
connector.
AC±54±
AIR CONDITIONING SYSTEM Troubleshooting
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INSPECTION PROCEDURE
Check compressor
(1). Check compressor drive belt tension (See page AC-104).
(2). Check if the compressor does not lock during with engine started and blo\
wer switch and A/C switch ON.
Adjust drive belt tension or repair compressor.
Check compressor lock sensor.
Disconnect compressor lock sensor connector.
Measure resistance between terminals 1 and 2 of
compressor lock sensor connector.
Resistance:at 25°C (77°F) : 530 ±650

at 100°C (212°F) : 670 ±890

Replace compressor lock sensor.
Check for open and short in harness and connectors between air conditioner
control assembly and compressor lock sensor (See page IN-27).
Repair or replace harness or connector.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).However,
when Diag. code 22 is displayed, check and
replace air conditioner control assembly.
±
AIR CONDITIONING SYSTEM TroubleshootingAC±55
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Diag. Code 31, 41Air Mix Damper Position Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the position of the air mix
damper and sends the appropriate signals to the
air conditioner control assembly.
The position sensor is built into the air mix servo-
motor assembly.
Code No.Diag. Code Detecting ConditionTrouble area
31Short to ground or power source circuit in air
mix damper position sensor circuit.
Air mix damper position sensor

Harness or connector between air mix
servomotor assembly and A/C control
41
Air mix damper position sensor value does
not change even if A/C control assembly
operates air mix servomotor.servomotor assembly and A/C control
assembly.

A/C control assembly
DIAGNOSTIC CHART
Check voltage between terminals TP and
SG of air conditioner control assembly
connector.
Check air mix damper position sensor.
Check harness and connector between air
conditioner control assembly and air mix
servomotor assembly (See page IN-27).
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36 ). However, when Diag.
code31 or 41 is displayed, check
and replace air conditioner control
assembly.
Replace air mix servomotor
assembly.
Repair or replace harness or
connector.
AC±58±
AIR CONDITIONING SYSTEM Troubleshooting
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