engine LEXUS SC400 1991 Service Owner's Manual

LOCATION OF CONNECTORS
LOCATION OF CONNECTORS IN ENGINE COMPARTMENT
AC±38±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

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

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
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

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
±
AIR CONDITIONING SYSTEM TroubleshootingAC±61
WhereEverybodyKnowsYourName

\
\


\

\
\
Igniter Circuit
CIRCUIT DESCRIPTION
The air conditioner control assembly monitors the engine speed through sign\
als sent from the igniter.
The air conditioner control assembly uses these signals and compressor speed signals to detect the
compressor lock condition.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check operation of tachometer.
Check harness and connector between air
conditioner control assembly and igniter
(See page IN-27).
Proceed to combination meter
troubleshooting (See page
BE-125 ).
Proceed to next circuit inspection
shown on matrix chart (See page AC-36).
Repair or replace harness or
connector.
AC±82±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

\
\


\

\
\
Compressor Circuit
CIRCUIT DESCRIPTION
The air conditioner control assembly outputs the magnetic clutch ON signal \
from terminal MGC to the
Engine & ECT ECU.
When the Engine & ECT ECU receives this signal, it sends a signal from terminal A\
CMG and switches
the air conditioner magnetic clutch relay on, thus turning on the air condi\
tioner compressor magnetic
clutch.
The air conditioner control assembly also monitors at terminal A/C IN wheth\
er or not power is being sup-
plied to the magnetic clutch.
DIAGNOSTIC CHART
See next page for the Diagnostic Chart.
WIRING DIAGRAM
AC±84±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

Check voltage between terminals A/C IN of air
conditioner control assembly connector and
body ground .
Check A/C compressor magnetic clutch.
Check harness and connector between
A/C compressor and compressor relay
(See page IN-27).
Proceed to next circuit inspection
shown on matrix chart (See page AC-36).
Check voltage between terminals MGC of air
conditioner control assembly connector and
body ground .
Check voltage between terminals MGC of air
conditioner control assembly harness side con-
nector and body ground .
Check harness and connector between
air conditioner control assembly and
engine & ECT ECU (See page iN±27).
Check and replace engine & ECT ECU.
Check magnetic clutch relay.
Repair A/C compressor magnetic
clutch.
Repair or replace harness or
connector.
Check and replace air conditioner
control assembly.
Repair or replace harness or
connector.
Replace magnetic clutch relay.
Check voltage between terminals ACMG of
engine & ECT ECU and body ground .
Check harness and connector between
engine & ECT ECU and battery (See page
IN-27).
Check and replace engine & ECT ECU.
Repair or replace harness or
connector.
Check harness and connector between
air conditioner control assembly and
compressor relay, compressor relay and
battery (See page IN±27 ).
Repair or replace harness or
connector.
Check and replace air conditioner control
assembly.
±
AIR CONDITIONING SYSTEM TroubleshootingAC±85
WhereEverybodyKnowsYourName

Check voltage between terminals A/C IN of air conditioner control
assembly connector and body ground.
(1) Remove console upper panel.(See pageBO-111 ).
(2) Remove A/C control assembly with
connectors still connected.
(3) Start the engine.
Check voltage between terminals A/C IN of air condi-
tioner control assembly and body ground when mag-
netic clutch is on and off by A/C switch
Go to step (4).
Check air conditioner compressor magnetic clutch.
Disconnect magnetic clutch connector.
Connect positive
lead connected to battery to mag-
netic clutch connector terminal 3.
Magnetic clutch is energized.
Repair air conditioner compr essor magnetic
clutch.
Check for open and short in harness and connecter between air
conditioner compressor and compressor relay (See page IN-27).
Repair or replace harness or connector.
Proceed to next circuit inspection shown on ma-
trix chart (See page AC-36).
INSPECTION PROCEDURE
AC±86±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName