Lexus SC300 / Lexus SC400. Manual - part 140

DEFOGGER SYSTEM

Description

The component parts of this system and their functions are described in the following table.

Parts Name

Function

Defogger

When over current flows in the defogger circuit, the Defogger fuse breaks the circuit
to protect it against damage.

Defogger Relay

This relay is supplied with current from terminal IG1 of ignition switch (Ignition switch ON)
and switches large current from the defogger.

A/C Control Panel
Assembly

 Defogger Switch

The defogger switch is built into the A/C Control Panel Assembly. This switch is
supplied with current from the relay and fuse HTR. Grounds current from the defogger
relay, turning the defogger relay ON.

Defogger

 Rear Window

 Outer Mirror

These defoggers generate heat when current is supplied from the defogger relay.

Parts Location

–

BODY ELECTRICAL SYSTEM

Defogger System

BE–171

Wiring and Connector Diagrams

Parts Inspection
(Defogger Switch)
REMOVAL AND INSTALLATION OF AIR
CONDITIONER CONTROL PANEL
ASSEMBLY

(See Instrument Panel on page 

BO–111

)

INSPECTION OF DEFOGGER SWITCH

INSPECT SWITCH OPERATION

(a) Connect 

the positive (+) lead from the battery to terminal

A6 and negative (–) lead to terminal A7.

(b) Connect 

the positive (+) lead from the battery to terminal

B10 through a 1.4 W test bulb.

BE–172

–

BODY ELECTRICAL SYSTEM

Defogger System

(c)  Turn the defogger switch ON and check that the test

bulb and indicator light turn ON, then turn OFF after
about 15 minutes.

If operation is not as specified, replace the air conditioner
control panel assembly.

(Defogger Relay)
INSPECTION OF DEFOGGER RELAY

INSPECT RELAY CONTINUITY AND OPERATION

Terminal

Condition

Constant

Apple battery voltage

to terminals 1 and 3.

If continuity is not as specified, replace the relay.

(Defogger Wires)
INSPECTION AND REPAIR OF
DEFOGGER WIRES

1. 

INSPECT DEFOGGER WIRES
NOTICE:

•

VWhen cleaning the glass, use a soft, dry cloth, and wipe

the glass in the direction of the wire. Take care not to

damage the wires.

•

VDo not use detergents or glass cleaners with abrasive

ingredients.

•

VWhen measuring voltage, wind a piece of tin foil around

the top of the negative probe and press the foil against

the wire with your finger as shown.

(a)  Turn the ignition switch ON.
(b)  Turn the defogger switch ON.
(c)  Inspect the voltage at the center of each heat wire as

shown.

Voltage

Criteria

Approx. 5 V

Okay (No break in wire)

Approx. 10 V or 0 V

Broken wire

HINT: If there is approximately 10 volts, the wire is broken be-
tween the center of the wire and the positive (+) end. If there
is no voltage, the wire is broken between the center of the
wire and ground.

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BODY ELECTRICAL SYSTEM

Defogger System

BE–173

(d) Place the voltmeter positive (+) lead against the

defogger positive (+) terminal.

(e)  Place the voltmeter negative (–) lead with the foil strip

against the heat wire at the positive (+) terminal end and
slide it toward the negative (–) terminal end.

(f)  The point where the voltmeter deflects from zero to

several volts is the place where the heat wire is broken.

HINT: IF the heat wire is not broken, the voltmeter indicates
0 volts at the positive (+) end of the heat wire but gradually
increases to about 12 volts as the meter probe is moved to
the other end.

2. 

REPAIR DEFOGGER WIRES
(a)  Clean the broken wire tips with a grease, wax and

silicone remover.

(b)  Place the masking tape along both sides of the wire to

be repaired.

(c)  Thoroughly mix the repair agent (Dupont paste No.

4817).

(d)  Using a fine tip brush, apply a small amount to the wire.
(e)  After a few minutes, remove the masking tape.
(f)  Allow the repair to stand at least 24 hours.

(Mirror Defogger)
REMOVAL AND INSTALLATION OF
MIRROR ASSEMBLY

(See Outside Rear View Mirror on page 

BO–42

).

BE–174

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BODY ELECTRICAL SYSTEM

Defogger System