Lexus SC300 / Lexus SC400. Service manual — part 943

TROUBLE SHOOTING:

Use the matrix chart below as a guide to repairs. Verify necessary inputs to the A/C Control Assembly from
the vehicle prior to disassembly. Use the repair manual, A/C system section, to validate such as B+, ILL+,
ground, etc..

SUSPECT AREA

SYMPTOM

Control

Switch

Indicator

Panel

Control

Lamp Circuit

Night Illumination does not

come on

LCD back lighting does not

come on

Indicator lamps of all

switches are off

Indicator lamp of all

switches are on

LCD is faulty

NOTE:

If symptoms still exist after the suspect areas have been tested and found not to be
faulty, replace the amplifier.

1

LCD illumination bulbs are not serviceable, Control Switch must be replaced if illumination
does not occur.

AIR CONDITIONING CONTROL DISASSEMBLY:

1. Remove Air Conditioning Control Assembly.

2. Separate Control Panel from case.

a. Cut the cloth tape on both sides of the case

(See Fig. 2).

1992 - 1995 SC 300/400 A/C CONTROL ASSEMBLY SERVICE PARTS

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Bulb Switch

D

D

1

D

D

D

D

1992 - 1995 SC 300/400 A/C CONTROL ASSEMBLY SERVICE PARTS

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AIR CONDITIONING CONTROL DISASSEMBLY (Cont’d):

b. Remove 2 screws and release the 6 clips to

separate the Control Panel from the case.

c. Disconnect 2 connectors to separate the

Control Panel from the case.

d. Remove the wire harness (See Fig. 5).

3. Remove Control Switch.

a. To replace the Control Switch remove 2

screws and release 4 clips (See Fig. 6).

b. Separate Control Switch from face plate.

4. Replace the Night Illumination Bulb.

Using a flat–bladed screwdriver, remove and
replace the Night Illumination Bulb.

1992 - 1995 SC 300/400 A/C CONTROL ASSEMBLY SERVICE PARTS

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INSPECTION PROCEDURE:

1. Bulb Circuit:

D

Bulb Inspection – Perform the following test
on suspect Night Illumination Bulbs. Check
for continuity as shown. Replace the bulb if
there is no continuity.

D

Bulb Circuit Inspection – Verify continuity
between terminals 22 and 24. If there is
no continuity, replace Control Switch.

2. Switch Circuit:

D

Switch Continuity Inspection – Check that there
is continuity between the terminals while the
switch is pressed.

D

If there is no continuity between even one pair
of terminals, replace the Control Switch.

SWITCH

A/C

MODE/R>

MODE/L<

REAR - DEF

FRONT - DEF

FRESH

RECIRC

OFF

FAN - DOWN

FAN - UP

13 - 17

13 - 16

13 - 15

12 - 17

12 - 16

12 - 15

12 - 14

11 - 17

11 - 16

11 - 15

INSPECTION

TERMINALS

1992 - 1995 SC 300/400 A/C CONTROL ASSEMBLY SERVICE PARTS

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INSPECTION PROCEDURE (Cont’d):

3. Indicator Lamp Circuit:

D

Connect two 1.5 v dry cell
batteries in series. Using the
table, check that each suspect
indicator lamp illuminates.

NOTE:

Since the indicator lamps
are LEDs, do not mix the “+”
and “–” terminals of the test
batteries or apply power to
them for more than 3 seconds
at a time.

D

If a suspect LED does not illuminate
when tested, replace the Control Switch.

INDICATOR

A/C

REAR - DEF

FRONT - DEF

FRESH

RECIRC

TERMINAL TO

CONNECT “+”

10

20

20

19

19

TERMINAL TO
CONNECT “-”

18

18

8

18

8