sensor LEXUS SC400 1991 Service User Guide

Blower Fan Speed Control System
(When AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and thetemperature setting, the air conditioner control ECU determines the air flow volume\
and outputs signals
to the power transistor.
(c) When it receives signals from the ECU, the power transistor increases or red\
uces the blower motor speed to control the air flow volume.
(When AUTO Switch is OFF)
The ECU turns the power transistor increasing or reducing the blower mot\
or speed fixing the air flow volume
in accordance with the position of the Manual switch. AC±10
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AIR CONDITIONING SYSTEM Description
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Air Flow Mode Control System
(When the AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and thetemperature setting, the air conditioner control ECU determines the air flow mode a\
nd outputs signals to
the mode servomotor and max cool servomotor.
(c) When it receives signals from the ECU, the servomotors open or close each of\
the dampers to change the air flow mode.
(When the AUTO Switch is OFF)
The ECU fixes the air flow mode in accordance with the Manual switch pos\
ition.
(When the Engine is Cold)
If the Mode is set on B/L or FOOT, the ECU forcedly changes the air vent to DEF if cold signals are input from
the water temperature sensor.
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AIR CONDITIONING SYSTEM DescriptionAC±11
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Air Inlet Control System
(When the AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and thetemperature setting, the air conditioner control ECU determines the air \
inlet and outputs signals to the air
inlet servomotor assembly.
(c) When it receives signals from the ECU, the air inlet servomotor opens or clo\
ses the damper to change the air inlet. When the air inlet is changed to the desired setting, it is detected by the air inlet damper p\
osition
sensor and the ECU stops the servomotor.
HINT: If the Mode switch is set on DEF, the ECU forcedly changes the air inlet to FRS.
(When the AUTO Switch is OFF)
The ECU fixes the air inlet according to the position of the manual swit\
ch. AC±12
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AIR CONDITIONING SYSTEM Description
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HOW TO PROCEED WITH TROUBLESHOOTING
Perform troubleshooting in accordance with the procedure on the following page.\
[1] CUSTOMER PROBLEM ANALYSIS Using the customer problem analysis check sheet for reference, ask the c\
ustomer in as much detail as
possible about the problem. A subjective complaint such as ºpoor air conditio\
ner efficiencyº is also consid-
ered in the air conditioner complaints.
Therefore, in ºCustomer Problem Analysisº and ºProblem Symptom Confirmationº\
, check carefully to deter-
mine whether the level of performance is the actual (normal) level or whet\
her it is abnormal. Then perform
troubleshoot accordingly.
[2] CHECK AND CLEAR THE DIAGNOSTIC CODES (PRECHECK) First check the diagnostic codes to see if there are any malfunction cod\
es stored in memory. If there are
malfunction codes, make a note of them, then clear them and proceed to [3] problem \
Symptom Confirma-
tionº.
[3] PROBLEM SYMPTOM CONFIRMATION, [4] SYMPTOM SIMULATION Confirm the problem symptoms. If the problem does not reappear, be sure to simulate the problem by main-
ly checking the circuits indicated by the diagnostic code in step [2], u\
sing ºProblem Simulation Methodº.
[5] DIAGNOSTIC CODE CHECK
Check the diagnostic codes. Check for problems with the sensors or the w\
ire harness.
[6] DIAGNOSTIC CODE CHART If a malfunction code is confirmed in the diagnostic code check, proceed t\
o the check procedure indicated
by the matrix chart for each diagnostic code.
[7] MATRIX CHART OF PROBLEM SYMPTOMS
If the normal code is confirmed in the diagnostic code check, perform in\
spection in accordance with the
inspection order in the matrix chart of problem symptoms.
[8] CIRCUIT INSPECTION Proceed with diagnosis of each circuit in accordance with the inspection order c\
ofirmed in [6] and [7]. Deter-
mine whether the cause of the problem is in the sensor, actuators, wire harness and connectors, or the
ECU.
[9] ACTUATOR CHECK Check actuators for proper operation. Instructions for this diagnosis ar\
e given in the flow chart for each
circuit.
[10] REPAIRS After the cause of the problem is located, perform repairs by following the i\
nspection and replacement pro-
cedures in this manual.
[11] CONFIRMATION TEST
After completing repairs, confirm not only that the malfunction is elimi\
nated, but also perform diagnostic
code check and actuator check, etc. again to make sure the entire air condit\
ioning system is operating cor-
rectly.
AC±22
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AIR CONDITIONING SYSTEM REPAIR INSTRUCTIONS
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DIAGNOSIS SYSTEM
Warning for A/C compressor lock
If compressor lock occurs during air conditioner operation, the
( A/C ) switch indicator on the air conditioner control assembly
starts blinking to warn the driver.
When this occurs, check for compressor lock (code 22) using diag-
nostic code check then proceed to inspect the circuit or the com-
ponent.
Compressor lock sensor circuit page AC±54.
LIST OF OPERATION METHODS
By operating each of the air conditioner control switches as shown in the \
diagram below, it is possible to enter
the diagnosis check mode. AC±26
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AIR CONDITIONING SYSTEM Troubleshooting
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INDICATOR
1. Turn the ignition switch on while pressing the ari conditioner control
switch and REC swich
simultaneously.
2. Check that all the indicators light up and go off at 1 second intervals 4 times in succession.
3. Check that the buzzer sounds when the indicators light up in 2.
HINT:
wAfter the indicator check is ended, the diagnostic code
check begins automatically.
w Press the OFF switch when desiring to cancel the check
mode.
DIAGNOSTIC CODE CHECK (SENSOR
CHECK)
1. Perform an indicator check. After the indicator check is completed, the system enters the diagnostic code check
mode automatically.
2. Read the code displayed on the panel. Refer to the list of
codes on page AC±28 when reading the codes. (Codes are
output at the temperature display.)
If the slower display ped is desired, press the FRS
switch and change it to stepped operation. Each time the
FRS
switch is pressed, the display changes by 1 step.
HINT:
w If the buzzer sounds when a code is being read, it means
the trouble indicated by that code continues to occur.
w If the buzzer does not sound when a code is being read,
it means the trouble indicated by that code occurred ear-
lier (such as poor connector contacts, etc.)
CLEARING DIAGNOSTIC CODES
1. Pull out the DOME fuse in Relay Block No. 2 for 10 sec. or
longer to clear the memory of diagnostic codes.
2. After reinserting the fuse, check that the normal code is output.
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AIR CONDITIONING SYSTEM TroubleshootingAC±27
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DIAGNOSTIC CODE CHART
If a malfunction code is displayed during the diagnostic code check (sens\
or check), check the circuit listed for
that code in the table below (Proceed to the page given for that circuit.)\
Code No.Diag. Code Detecting Condition
00 Normal
11 *1 Open or short in room temperature sensor circuit.
12 Open or short in ambient temperature sensor circuit.
13 Open or short in evaporator temperature sensor circuit.
14*2 Open or short in water temperature sensor circuit.
21*3 Open in solar sensor circuit.
21*3
 Short in solar sensor circuit.
22*4
 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 c\
omparison to normal
operation.
23
 Open in pressure sensor circuit.
 Abnormal refrigerant pressure below 206 kPa (2.1 kgf/cm, 30 psi)
over 2,650 kPa (27 kgf/cm, 385 ps\
i)
31 Short to ground or power source circuit in Air Mix Damper position sens\
or circuit.
32 Short to ground or power source circuit in Air Inlet Damper position se\
nsor circuit.
33 Short to ground or power source circuit in Air Outlet Damper position s\
ensor circuit.
41 Air mix damper position sensor value does not change even if ECU operat\
es air mix servomotor.
42 Air inlet damper position sensor value does not change even if ECU oper\
ates air inlet servomotor.
43 Air outlet damper position sensor value does not change even if ECU ope\
rates air outlet
servomotor.
HINT: *1 If the room temp. is approx. ±20 °C (±4 °F) or lower, code 11 may be output even though the system
is normal.
*2 If the ambient temperature is approx. ±50 °C (±58 °F) or lower, a malfunction code may be output
even though the system is normal.
*3 If the check is being performed in a dark place, diagnostic code 21 (so\
lar sensor circuit abnormal) could be displayed.
In this case, perform diagnostic code check again while shining a light,\
such as an inspection light,
on the solar sensor.
If code 21 is still displayed, there could be trouble in the solar senso\
r circuit
AC±28
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AIR CONDITIONING SYSTEM Troubleshooting
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Trouble AreaMemory*5See page
±±±
 Room temp. Sensor
 Harness or connector between room temp. sensor and A/C control assembly\
 A/C control assemblyO
(8.5 min. or more)AC±44
 Ambient temp. sensor
 Harness or connector between ambient temp. sensor and A/C control assem\
bly
 A/C control assemblyO
(8.5 min. or more)AC±46
 Evaporator temp. sensor
 Harness or connector between evaporator temp. sensor and A/C control
assembly A/C control assemblyO
(8.5 min. or more)AC±48
 Water temp. sensor
 Harness or connector between water temp. sensor and A/C control assembl\
y
 A/C control assemblyO
(8.5 min. or more)AC±50
 Solar sensor
H b d A/C l bl
±
AC 52 Solar sensor
 Harness or connector between sensor and A/C control assembly
 A/C control assemblyOAC±52
 A/C control assemblyO
(8.5 min. or more)
 Compressor drive belt Compressor lock sensor Compressor
 Harness and connector between A/C control assembly and compressor,
 compressor lock sensor
 A/C control assembly
±AC±54
 Pressure switch
 Harness or connector between pressure switch and A/C control assembly
 Refrigerant pipe line
 A/C control assembly
±AC±56
 Air mix damper position sensor A/C control assembly
 Harness or connector between air mix damper position sensor and
A/C control assemblyO
(1 min. or more)AC±58
 Air inlet damper position sensor A/C control assembly
 Harness or connector between air inlet damper position sensor and
A/C control assemblyO
(1 min. or more)AC±62
 Air outlet damper position sensor A/C control assembly
 Harness or connector between air outlet damper position sensor and
A/C control assemblyO
(1 min. or more)AC±66
 Air mix servomotor Air mix damper position sensor
 Harness and connector between A/C control assembly and air mix position\
sensor
 Harness and connector between A/C control assembly and air mix servomot\
or.O
(15 secs. or more)AC±58
AC±60
 Air inlet servomotor Air inlet damper position sensor
 Harness and connector between A/C control assembly and air inlet positi\
on sensor.
 Harness and connector between A/C control assembly and air inlet servom\
otor.O
(15 secs. or more)AC±62
AC±64
 Air outlet servomotor Air outlet damper position sensor
 Harness and connector between A/C control assembly and air outlet posit\
ion
sensor.
 Harness and connector between A/C control assembly and air outlet servo\
motor.
 A/C control assembly
O
(15 secs. or more)AC±66
AC±68
±
AIR CONDITIONING SYSTEM TroubleshootingAC±29
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AC±44AC±46AC±48AC±50AC±52AC±54AC±56AC±58AC±60AC±62AC±64AC±66
MATRIX CHART OF PROBLEM SYMPTOMS
If a normal code is displayed during the diagnostic code check (sensor ch\
eck) but the trouble still occurs (reap-
pears), perform out troubleshooting for each problem symptom, checking the circuits for each symptom in the
order given in the table below (Proceed to the page given for each circuit)\
. AC±36
±
AIR CONDITIONING SYSTEM Troubleshooting
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Check voltage between terminals TR
and SG of air conditioner assembly
connector.
Check room temperature sensor.
Check harness and connector between air
conditioner control assembly and room tem-
perature sensor (See page IN-27).
Check and repair air conditioner control
assembly. 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.
Replace room temperature sensor.
Repair or replace harness or
connector.
CIRCUIT INSPECTION
Diag. Code 11Room Temperature Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the temperature inside the cabin and sends the appropria\
te signals the A/C control
assembly.
Code No.Diag. Code Detecting ConditionTrouble area
11
Open or short in room temperature sensor
circuit.
Room temperature sensor.

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

A/C control assembly.
DIAGNOSTIC CHART
AC±44±
AIR CONDITIONING SYSTEM Troubleshooting
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