LEXUS SC400 1991 Service Owners Manual

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
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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
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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±
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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.
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AIR CONDITIONING SYSTEM TroubleshootingAC±55
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Diag. Code 23Compressor Lock Sensor Circuit
CIRCUIT DESCRIPTION
The pressure switch sends the appropriate signals to the air conditioner co\
ntrol assembly when the air
conditioner refrigerant pressure drops too low or rises too high. When the air cond\
itioner control assem-
bly receives these signals, it outputs signals via the Engine & ECT ECU to switch off the compressor
relay and turns the magnet clutch off.
Code No.Diag. Code Detecting ConditionTrouble area
23

Open in pressure sensor circuit.

Abnormal refrigerant pressure.
below 206 kPa (2.1 kgf/cm
2, 30 psi)
over 2,650 kPa (27 kgf/cm2, 385 psi)

Pressure switch.

Harness or connector between pressure switch
and ECU. Refrigerant pipe line.

ECU.
DIAGNOSTIC CHART
Check voltage between terminals LP of air
conditioner control assembly and body
ground.
Check pressure switch.
Check harness and connector between air
conditioner control assembly and pressure
switch and body ground
(See page IN-27).
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36 ).
Replace pressure switch
Repair or replace harness or
connector.
AC±56±
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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
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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±
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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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Diag. Code 41Air Mix Servomotor Circuit
CIRCUIT DESCRIPTION
The air mix servomotor is controlled by the A/C control assembly and moves \
the air mix damper to the
desired position.
Code No.Diag. Code Detecting ConditionTrouble area
41
Air mix damper position sensor value does not
change even if A/C control assembly operates
air mix servomotor.
Air mix servomotor.

Air mix damper position sensor.

Harness or connector between A/C controlas-
sembly and A/M servomotor, A/M damperposi-
tion sensor.

A/C control assembly.
DIAGNOSTIC CHART
Actuator check.
Check air mix servomotor.
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
show on matrix chart (See page
AC-36 ).
Replace air mix servomotor
assembly.
Repair or replace harness or
connector.
AC±60±
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Actuator check.
(1) Warm up the engine.
(2) Set to the actuator check mode (See pageAC-30 ).
(3) Press the FRS switch and change it to step operation.
Press the FRS switch and check the
operation of the air mix damper and the condition
of the blower.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).
Check air mix servomotor.
Remove heater unit.
Connect positive
lead to terminal 4 and negative
 lead to terminal 5.
The lever turns smoothly to cool side.
Connect negative  lead to terminal 4 and positive

lead to terminal 5.
The lever turns smoothly to hot side.
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±61
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