Lexus SC300 / Lexus SC400. Service manual — part 960

141

: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR

CODE

SEE PAGE

JUNCTION BLOCK AND WIRE HARNESS (CONNECTOR LOCATION)

1B

20

ENGINE ROOM MAIN WIRE

1E

20

INSTRUMENT PANEL WIRE

1H

1I

20

COWL WIRE

1J

20

COWL WIRE

3A
3B
3D

22

INSTRUMENT PANEL WIRE

3E

22

INSTRUMENT PANEL WIRE

3F
3H

: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS

CODE

SEE PAGE

JOINING WIRE HARNESS AND WIRE HARNESS (CONNECTOR LOCATION)

EB1

34

ENGINE WIRE AND ENGINE ROOM MAIN WIRE (FRONT SIDE OF R/B NO. 2)

IE1

36

ENGINE ROOM MAIN WIRE AND COWL WIRE (R/B NO. 4)

IE2

36

ENGINE ROOM MAIN WIRE AND COWL WIRE (BEHIND GLOVE BOX)

IG1

36

INSTRUMENT PANEL WIRE AND COWL WIRE (R/B NO. 5)

IG3

36

INSTRUMENT PANEL WIRE AND COWL WIRE (RIGHT KICK PANEL)

IJ1

36

ENGINE WIRE AND COWL WIRE (RIGHT KICK PANEL)

IJ2

36

ENGINE WIRE AND COWL WIRE (RIGHT KICK PANEL)

IK1

36

ENGINE WIRE AND INSTRUMENT PANEL WIRE (RIGHT KICK PANEL)

IK2

36

ENGINE WIRE AND INSTRUMENT PANEL WIRE (RIGHT KICK PANEL)

IO1

38

ENGINE ROOM MAIN WIRE AND INSTRUMENT PANEL WIRE (RIGHT KICK PANEL)

BW1

40

ENGINE ROOM MAIN WIRE AND FLOOR NO. 3 WIRE (RIGHT KICK PANEL)

Bc2

40

FLOOR NO. 3 WIRE AND FLOOR WIRE (UNDER THE LEFT SIDE OF REAR SEAT CUSHION)

: GROUND POINTS

CODE

SEE PAGE

GROUND POINTS LOCATION

EA

34

FRONT SIDE OF RIGHT FENDER

EB

34

FRONT SIDE OF LEFT FENDER

ED

34

REAR SIDE OF INTAKE MANIFOLD

IF

36

LEFT KICK PANEL

IJ

36

RIGHT KICK PANEL

: SPLICE POINTS

CODE

SEE PAGE

WIRE HARNESS WITH SPLICE POINTS

CODE

SEE PAGE

WIRE HARNESS WITH SPLICE POINTS

E 2

I23

38

INSTRUMENT PANEL WIRE

E 7

I25

38

ENGINE ROOM MAIN WIRE

E 9

34

ENGINE ROOM MAIN WIRE

ENGINE ROOM MAIN WIRE

I26

38

ENGINE ROOM MAIN WIRE

E10

34

ENGINE ROOM MAIN WIRE

ENGINE ROOM MAIN WIRE

I32

E12

I33

E13

I35

38

ENGINE WIRE

E18

34

ENGINE WIRE

I36

38

ENGINE WIRE

E20

34

ENGINE WIRE

I37

I 4

B17

40

FLOOR NO. 3 WIRE

I 7

38

COWL WIRE

B34

40

FLOOR MAIN WIRE

I14

38

COWL WIRE

B36

40

FLOOR NO. 3 WIRE

I16

38

INSTRUMENT PANEL WIRE

142

ABS AND TRACTION CONTROL

226

AUTOMATIC AIR CONDITIONER

1. HEATER BLOWER MOTOR OPERATION

CURRENT IS APPLIED AT ALL TIMES THROUGH HEATER FUSE (60A) TO TERMINAL 5 OF HEATER RELAY. WHEN THE IGNITION SW IS
TURNED ON, CURRENT FLOWS THROUGH HEATER FUSE (10A) TO TERMINAL 1 OF HEATER RELAY

→

TERMINAL 3

→

TERMINAL HR

OF A/C CONTROL ASSEMBLY. AT THE SAME TIME, CURRENT ALSO FLOWS FROM HEATER FUSE (10A) TO TERMINAL IG+ OF A/C
CONTROL ASSEMBLY AND TERMINAL 2 OF WATER VALVE VSV

→

TERMINAL 1

→

TERMINAL WV OF A/C CONTROL ASSEMBLY.

∗

LOW SPEED OPERATION

WHEN THE BLOWER SW (A/C CONTROL ASSEMBLY) IS PUSHED TO LOW SPEED POSITION, THE CURRENT TO TERMINAL HR OF A/C
CONTROL ASSEMBLY FLOWS TO TERMINAL E OF A/C CONTROL ASSEMBLY

→

GROUND AND TURNS THE HEATER RELAY. AS A

RESULT, THE CURRENT TO TERMINAL 5 OF HEATER RELAY FLOWS TO TERMINAL 4 OF RELAY

→

TERMINAL 2 OF BLOWER

RESISTOR

→

TERMINAL 1

→

GROUND AND CAUSES THE BLOWER MOTOR TO ROTATE AT LOW SPEED.

∗

MEDIUM (M1, M2, M3) AND HIGH SPEED OPERATION

WHEN THE BLOWER SW (A/C CONTROL ASSEMBLY) IS SELECTED TO MEDIUM (M1, M2, M3) OR HIGH POSITION, THE CURRENT TO
TERMINAL HR OF A/C CONTROL ASSEMBLY FLOWS TO TERMINAL E

→

GROUND AND TURNS THE HEATER RELAY ON. THEN, THE

CURRENT TO TERMINAL IG+ OF A/C CONTROL ASSEMBLY FLOWS TO TERMINAL BLR

→

TERMINAL (B)2 OF POWER TRANSISTOR

→

TERMINAL (A)1

→

GROUND. AS A RESULT, THE CURRENT TO TERMINAL 5 OF HEATER RELAY FLOWS TO TERMINAL 4

→

TERMINAL 2 OF BLOWER MOTOR

→

TERMINAL 1

→

TERMINAL (A)2 OF POWER TRANSISTOR

→

TERMINAL (A)1

→

GROUND AND

BLOWER MOTOR IS ROTATED AT SELECTED SPEED BY THE A/C CONTROL ASSEMBLY CONTROLLING THE CURRENT FLOW FROM
TERMINAL (B)2 OF POWER TRANSISTOR TO TERMINAL (B)1.

∗

AUTO FUNCTION

WHEN THE AUTO SW IN HEATER CONTROL SW (A/C CONTROL ASSEMBLY) IS SELECTED, THE CURRENT FLOW IS THE SAME AS
ABOVE MENTIONS, BUT THE A/C CONTROL ASSEMBLY DECIDES THE APPROPRIATE AIR FLOW VOLUME ACCORDING TO SET
TEMPERATURE AND THE INPUT SIGNALS FROM EACH SENSOR. BY CONTROLLING THE CURRENT FLOW FROM TERMINAL BLR OF
THE A/C CONTROL ASSEMBLY TO TERMINAL (B)2 OF POWER TRANSISTOR

→

TERMINAL (A)1

→

GROUND, THE A/C CONTROL

ASSEMBLY CONTROLS THE BLOWER MOTOR STEPLESSLY.

2. OPERATION OF AIR INLET CONTROL SERVO MOTOR

(SWITCHING FROM FRESH TO RECIRC)

WITH IGNITION SW TURNED ON, THE CURRENT FLOWS FROM HEATER FUSE (10A) TO TERMINAL IG+ OF A/C CONTROL ASSEMBLY

→

TERMINAL MREC

→

TERMINAL 6 OF AIR INLET CONTROL SERVO MOTOR

→

TERMINAL 2

→

TERMINAL MFRS OF A/C CONTROL

ASSEMBLY

→

TERMINAL E

→

GROUND, THE MOTOR ROTATES AND THE DAMPER MOVES TO THE RECIRC SIDE. WHEN THE

DAMPER OPERATES WITH THE A/C SW AT RECIRC POSITION, THE DAMPER POSITION SIGNAL IS INPUT FROM TERMINAL 5 OF THE
SERVO MOTOR TO TERMINAL TPI OF THE ECU (BUILT INTO THE A/C CONTROL ASSEMBLY). AS A RESULT, CURRENT TO THE SERVO
MOTOR CIRCUIT IS CUT OFF BY THE ECU, SO THE DAMPER STOPS AT THAT POSITION.

(SWITCHING FROM RECIRC TO FRESH)

WITH IGNITION SW TURNED ON, WHEN THE RECIRC/FRESH SW IS SWITCHED TO THE FRESH SIDE, THE CURRENT FLOWS FROM
TERMINAL IG+ OF A/C CONTROL ASSEMBLY

→

TERMINAL MFRS

→

TERMINAL 2 OF AIR INLET CONTROL SERVO MOTOR

→

TERMINAL 6

→

TERMINAL MREC OF A/C CONTROL ASSEMBLY

→

TERMINAL E

→

GROUND, THE MOTOR ROTATES AND THE

DAMPER STOPS AT THAT POSITION.

3. OPERATION OF AIR VENT MODE CONTROL SERVO MOTOR

WITH IGNITION SW TURNED ON, THE CURRENT FLOWS FROM HEATER FUSE (10A) TO TERMINAL IG+ OF A/C CONTROL ASSEMBLY.

(SWITCHING FROM DEF TO FACE)

THE CURRENT FLOWS FROM TERMINAL MFACE OF A/C CONTROL ASSEMBLY

→

TERMINAL 4 OF AIR VENT CONTROL SERVO

MOTOR

→

TERMINAL 5

→

TERMINAL MDEF OF A/C CONTROL ASSEMBLY

→

TERMINAL E

→

GROUND. THE MOTOR ROTATES AND

THE DAMPER MOVES TO THE FACE SIDE. WHEN THE DAMPER OPERATES WITH THE A/C SW AT FACE POSITION, THE DAMPER
POSITION SIGNAL IS INPUT FROM TERMINAL 1 OF THE SERVO MOTOR TO THE TERMINAL TPM OF THE ECU (BUILT INTO THE A/C
CONTROL ASSEMBLY). AS A RESULT, CURRENT TO THE SERVO MOTOR CIRCUIT IS CUT OFF BY THE ECU, SO THE DAMPER STOPS
AT THAT POSITION.

(SWITCHING FROM FACE TO DEF)

THE CURRENT FLOWS FROM TERMINAL DEF OF A/C CONTROL ASSEMBLY

→

TERMINAL 5 OF AIR VENT CONTROL SERVO MOTOR

→

TERMINAL 4

→

TERMINAL MFACE OF A/C CONTROL ASSEMBLY

→

TERMINAL E

→

GROUND, THE MOTOR ROTATES AND THE

DAMPER STOPS AT THAT POSITION.

SYSTEM OUTLINE

227

4. OPERATION OF AIR MIX CONTROL SERVO MOTOR

WHEN THE TEMPERATURE SW IS TURNED TO THE “COOL” SIDE, THE CURRENT FLOWS FROM TERMINAL MC OF A/C CONTROL
ASSEMBLY

→

TERMINAL 4 OF AIR MIX CONTROL SERVO MOTOR

→

MOTOR

→

TERMINAL 5

→

TERMINAL MH OF A/C CONTROL

ASSEMBLY

→

GROUND AND THE MOTOR ROTATES. THE DAMPER OPENING ANGLE AT THIS TIME IS INPUT FROM TERMINAL 1 OF

SERVO MOTOR TO TERMINAL TP OF A/C CONTROL ASSEMBLY, THIS IS USED TO DETERMINE THE DAMPER STOP POSITION AND
MAINTAIN THE SET TEMPERATURE.

WHEN THE TEMPERATURE CONTROL SW IS TURNED TO THE “HOT” SIDE, THE CURRENT FLOWS FROM SERVO MOTOR

→

TERMINAL MH OF A/C CONTROL ASSEMBLY

→

TERMINAL 5 OF AIR MIX CONTROL SERVO MOTOR

→

MOTOR

→

TERMINAL 1

→

TERMINAL MC OF A/C CONTROL ASSEMBLY, ROTATING THE MOTOR IN REVERSE AND SWITCHING THE DAMPER FROM “COOL” TO
“HOT” SIDE.

5. AIR CONDITIONER OPERATION

THE A/C CONTROL ASSEMBLY RECEIVES VARIOUS SIGNALS, I.E., THE ENGINE RPM FROM THE IGNITER, OUTLET TEMPERATURE
SIGNAL FROM THE A/C THERMISTOR, COOLANT TEMPERATURE FROM THE WATER TEMP. SENSOR AND THE LOCK SIGNAL FROM
THE A/C COMPRESSOR, ETC.

WHEN THE ENGINE IS STARTED AND THE A/C SW (A/C CONTROL ASSEMBLY) IS ON, A SIGNAL IS INPUT TO THE ECU. (BUILT IN THE
A/C CONTROL ASSEMBLY).

AS A RESULT, THE GROUND CIRCUIT IN A/C CONTROL ASSEMBLY IS CLOSED AND CURRENT FLOWS FROM HEATER FUSE (10A) TO
TERMINAL 2 OF MAGNETIC CLUTCH RELAY

→

TERMINAL 3

→

TERMINAL ACMG OF ENGINE AND ECT ECU

→

TERMINAL E OF A/C

CONTROL ASSEMBLY

→

GROUND, TURNING THE MAGNETIC CLUTCH RELAY ON, SO THAT THE MAGNETIC CLUTCH IS ON AND THE

A/C COMPRESSOR OPERATES.

AT THE SAME TIME, THE ENGINE AND ECT ECU DETECTS THE MAGNETIC CLUTCH IS ON AND THE A/C COMPRESSOR OPERATES.

OPEN DIRECTION TO AVOID LOWERING THE ENGINE RPM DURING A/C OPERATING.

WHEN ANY OF THE FOLLOWING SIGNALS ARE INPUT TO THE A/C CONTROL ASSEMBLY, THE CONTROL ASSEMBLY OPERATES TO
TURN OFF THE AIR CONDITIONING.

∗

ENGINE HIGH TEMP. SIGNAL IS HIGH.

∗

COOLANT HIGH TEMP. SIGNAL IS HIGH.

∗

A SIGNAL THAT THE TEMPERATURE AT THE AIR OUTLET IS LOW.

∗

A SIGNAL THAT THERE IS A LARGE DIFFERENCE BETWEEN ENGINE RPM AND COMPRESSOR RPM.

∗

A SIGNAL THAT THE REFRIGERANT PRESSURE IS ABNORMALLY HIGH OR LOW.