Lexus RX300 (MCU15). Service manual - part 406

I05291

GND

M–

M+

+B

SI

DI–854

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

3

Check blower motor control relay.

PREPARATION:
Remove blower motor control relay with connectors still con-
nected.
CHECK:
(a)

Turn ignition switch ON.

(b)

Operate blower motor (High blower speed).

OK:

Terminals

Standard Value

GND ↔ Body Ground

Continuity

+B ↔ Body Ground

Battery Voltage

+M ↔ Body Ground

Battery Voltage

M+ ↔ M–

Battery Voltage

SI ↔ Body Ground

1 – 3 V

NG

Replace blower motor relay.

OK

Repair or replace harness or connector.

I08353

Engine and ECT ECU

ACMG

E10

6

LG–B

2C

2

2

1

Heater
Relay

5

3

Engine Room J/B

MG CLT Relay

2E

3

B–Y

EB1

3

A3 
Compressor 
Magnetic Clutch

3

B–Y

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–855

LEXUS RX300   (RM785E)

Compressor Circuit

CIRCUIT DESCRIPTION

The A/C ECU (Combination meter ECU) outputs the magnetic clutch ON signal from terminal MGC to the
engine and ECT ECU. When the engine and ECT ECU receives this signal, it sends a signal from terminal
ACMG and switches the A/C magnetic clutch relay ON, thus turning the A/C compressor magnetic clutch
ON.

WIRING DIAGRAM

DI3G8–03

I08373

(–)

ACMG(+)

I05334

3

DI–856

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

1

Check voltage between terminal ACMG of engine and ECT ECU.

CHECK:
(a)

Start engine.

(b)

Push AUTO SW.

(c)

Measure voltage between terminal ACMG of engine and
ECT ECU connector and body ground when A/C switch
is ON and OFF.

OK:

A/C switch

Voltage

ON

10 – 4 V

OFF

0 V

OK

Check and replace engine and ECT ECU and/or
A/C ECU (Combination meter ECU).

NG

2

Check A/C compressor magnetic clutch.

PREPARATION:
Disconnect magnetic clutch connector.
CHECK:
Connect positive (+) lead connected to battery to magnetic
clutch connector terminal 3.
OK:

Magnetic clutch is energized.

NG

Repair A/C compressor magnetic clutch.

OK

–

DIAGNOSTICS

AIR CONDITIONING SYSTEM

DI–857

LEXUS RX300   (RM785E)

3

Check harness and connector between A/C compressor and compressor relay
(See page IN–32).

NG

Repair or replace harness or connector.

OK

4

Check harness and connector between compressor relay and engine and ECT
ECU (See page IN–32).

NG

Repair or replace harness or connector.

OK

5

Check harness and connector between engine and ECT ECU and A/C compres-
sor assembly (See page IN–32).

NG

Repair or replace harness or connector.

OK

Check and replace engine and ECT ECU and/
or A/C ECU (Combination meter ECU).