Lexus SC300 / Lexus SC400. Manual — part 30
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Power Transistor Circuit
CIRCUIT DESCRIPTION
The air conditioner control assembly controls the blower speed by varying the voltage at terminal BLW
which applies the base current to the power transistor.
The air conditioner control assembly also monitors the power transistor collector voltage at terminal VM,
to control blower air volume precisely.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check power transistor.
Check harness and connector between air
conditioner control assembly and power
transistor (See page
Proceed to next circuit inspection
shown on matrix chart (See page
Replace power transistor.
Repair or replace harness or
connector.
AC–78
–
AIR CONDITIONING SYSTEM
Troubleshooting
Check power transistor.
(1)
(2)
Disconnect power transistor connector.
(1)
Check test bulb lights up when battery and
resistor are connected to power transistor
connector as left illustration shows.
(2)
Measure resistance between terminal 2 and 3
(1)
The bulb lights up.
(2)
Resistance: 2.0– 2.4
k
Replace power transistor.
Check for open and short in harness and connector between air
conditioner control assembly and power transistor (See page
Repair or replace harness or connector.
Proceed to next circuit inspection shown on matrix
chart (See page
INSPECTION PROCEDURE
–
AIR CONDITIONING SYSTEM
Troubleshooting
AC–79
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Blower Motor Circuit
CIRCUIT DESCRIPTION
This is the power source for the blower motor.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check blower motor.
Check harness and connector between battery
and blower motor, blower motor and body ground
(See page IN–37).
Check blower resistor.
Replace blower motor.
Replace blower motor.
Replace blower resistor.
Repair or replace harness or
connector.
Proceed to next circuit inspection
shown on matrix chart (See page
AC–80
–
AIR CONDITIONING SYSTEM
Troubleshooting
Check blower motor.
Remove blower motor.(See page
Connect positive
lead connected to terminal 2 of
blower motor connector, negative
lead to
terminal 1.
Blower motor operates smoothly.
Replace blower motor.
Check blower resistor.
Disconnect blower resistor connector.
Measure resistance between terminals 1 and 2 of
blower resistor connector.
Resistance:
2.6 – 3.0
Replace blower resistor.
Check for open short in harness and connector between battery
and blower motor, blower motor and body ground (See page
Repair or replace harness or connector.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).
INSPECTION PROCEDURE
–
AIR CONDITIONING SYSTEM
Troubleshooting
AC–81
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