Lexus SC300 / Lexus SC400. Manual — part 31
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Igniter Circuit
CIRCUIT DESCRIPTION
The air conditioner control assembly monitors the engine speed through signals 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
Proceed to combination meter
troubleshooting (See page
Proceed to next circuit inspection
shown on matrix chart (See page
).
Repair or replace harness or
connector.
AC–82
–
AIR CONDITIONING SYSTEM
Troubleshooting
Check power transistor.
Check that the tachometer operates normally.
Proceed to combination meter trou-
bleshooting (See page
Proceed to next circuit inspection shown on matrix
chart (See page
Repair or replace harness or connector.
Check for open and short in harness and connector between air
conditioner control assembly and igniter (See page
INSPECTION PROCEDURE
–
AIR CONDITIONING SYSTEM
Troubleshooting
AC–83
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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 ACMG and switches
the air conditioner magnetic clutch relay on, thus turning on the air conditioner compressor magnetic
clutch.
The air conditioner control assembly also monitors at terminal A/C IN whether 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
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
Proceed to next circuit inspection
shown on matrix chart (See page
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
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
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
Repair or replace harness or
connector.
Check and replace air conditioner control
assembly.
–
AIR CONDITIONING SYSTEM
Troubleshooting
AC–85
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