1991 LEXUS SC300 display

Check voltage between terminals TR 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.
Voltage
at 25°C (77°F) : 1.8~2.2 V
at 40°C (104°F) : 1.2~1.6 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 room temperature sensor.
(1) Remove instrument finish lower No. 1 panel.
(See page Be-103).
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 room temperature sensor.
Check for open and short in harness and connector between air conditioner
control assembly and room temperature sensor (See page IN-27).
Repair or replace harness or connector.
Check and repair air conditioner control
assembly.
(2) Disconnect room0 temperature sensor
connector.
Check voltage between terminals 1 and 2 of
room temperature sensor connector at each tem±
perature.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±45
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Diag. Code 12Ambient Temperature Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the ambient temperature and sends the appropriate signal\
s to the A/C control
assembly.
Code No.Diag. Code Detecting ConditionTrouble area
12
Open or short in ambient temperature sensor
circuit.
Ambient temperature sensor.

Harness or connector between ambient
temperature sensor and A/C control assem-
bly.

A/C control assembly.
DIAGNOSTIC CHART
Check voltage between terminals TAM and
SG of air conditioner control assembly con-
nector.
Check ambient temperature sensor.
Check harness and connector between air
conditioner control assembly and ambient
temperature sensor. (See page IN-27).
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
shown on matrix chart (See
pageAC-36 ). However, when Diag.
code 12 is displayed, check and re-
place air conditioner control assembly.
Replace ambient temperature
sensor.
Repair or replace harness or
connector.
AC±46±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

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
±
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
WhereEverybodyKnowsYourName

(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
±
AIR CONDITIONING SYSTEM TroubleshootingAC±49
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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
WhereEverybodyKnowsYourName

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
±
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±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName