Mitsubishi Electric MSC-CB20VB, MSC-CB25VB, MSC-CB35VB Service Manual

SPLIT-TYPE, AIR CONDITIONERS
SPLIT-TYPE, HEAT PUMP AIR CONDITIONERS

INDOOR UNIT

SERVICE MANUAL

Wireless type
Models

No. OB439

MSC-CB20VB ­MSC-CB25VB ­MSC-CB35VB -

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB

E1

E1

E1

Outdoor unit service manual

MU-GA·VB Series (OB386)
MUH-GA·VB Series (OB387)
MUX-A·VB Series (OB384)
MXZ-A·WV Series (OB319)

CONTENTS

1. TECHNICAL CHANGES ····································2

2. PART NAMES AND FUNCTIONS······················3

3. SPECIFICATION·················································5

4. NOISE CRITERIA CURVES·······························6

5. OUTLINES AND DIMENSIONS·························7

6. WIRING DIAGRAM ············································8

7. REFRIGERANT SYSTEM DIAGRAM················8

8. SERVICE FUNCTIONS ······································9

9. TROUBLESHOOTING······································11

10. DISASSEMBLY INSTRUCTIONS·····················18

11. PARTS LIST······················································20

12. OPTIONAL PARTS ···········································22

NOTE:

•This manual describes technical data of indoor units.

1

TECHNICAL CHANGES

MSC-GA20VB - ➔ MSC-CB20VB -

MSC-GA25VB - ➔ MSC-CB25VB ­MSC-GA35VB - ➔ MSC-CB35VB -

1. Panel logo has been changed.

E1E1

E1E1

E1E1

2

2

Emergency operation switch

Fan

Catechin air filter
(With deodorizer)

Air outlet

Vertical vanes

Air inlet

to Breaker

Remote control
receiving section

Display section

Air cleaning filter(option)
(white bellows type)

Front panel

Power supply cord

Panel

Horizontal vane

Operation section

(When the front panel is opened)

Remote controller

Operation indicator lamp
Remote control

receiving section

PART NAMES AND FUNCTIONS

MSC-CB20VB MSC-CB25VB MSC-CB35VB

INDOOR UNIT

3

MSC-CB20VB

Installation plate
Installation plate fixing screw 4 o 25 mm
Remote controller holder
Fixing screw for 3 3.5 o 16 mm
Battery (AAA) for remote controller
Wireless remote controller
Felt tape (Used for left or left-rear piping)

1
5
1
2
2
1
1

<Indoor unit>

1

2

3

4

5

6

7

ON/OFF

FAN

TOO

WARM

TOO

COOL

VANE

MODE

ECONO COOL

STOP

START

HR.

MIN.

I FEEL

COOL

DRY

PM

CLOCK

AM

RESET

CLOCK

HEAT
/FAN

/

Open the front lid.

ON/OFF

TOO

COOL

PM

AM

TOO

WARM

Signal transmitting section

Operation display section

OPERATE /STOP
(ON /OFF) button

TEMPERATURE buttons

Indication of remote controller model is
on back.

OPERATION SELECT button

FAN SPEED CONTROL button

OFF-TIMER button

HR. button

MIN. button

(TIME SET button)

ON-TIMER button

RESET button

ECONO COOL button

VANE CONTROL button

CLOCK SET button

MSC-CB25VB
MSC-CB35VB

ACCESSORIES

REMOTE CONTROLLER

4

3

Indoor model

Function

Indoor unit power supply

Air flow(High/Med./Low)
Power outlet
Running current
Power input
Power factor
Fan motor current
Model
Winding
resistance (at 20:)
Dimensions WOHOD
Weight
Air direction
Sound level (High/Med./Low)
Fan speed (High/Med./Low)
Fan speed regulator
Remote controller model

K/h

A

A
W
%

A

"

mm

kg

dB

rpm

MSC-CB20VB

Single phase

230V,50Hz

10

0.17
35
90

0.17

RC4V19-JA

WHT-BLK 283

BLK-RED 188
815O278O244

9
5

3

KP1A

Cooling

474/372/276

36/31/25

900/750/600

Heating

510/420/342

36/31/25

950/820/700

MSC-CB25VB

Single phase

230V,50Hz

10

0.17
35
90

0.17

RC4V19-JA

WHT-BLK 283

BLK-RED 188
815O278O244

9
5

3

KP1A

Cooling

474/384/306

36/31/25

900/770/650

Heating

588/456/342

39/32/25

1,050/870/700

MSC-CB35VB

Single phase

230V,50Hz

10

0.19
40
92

0.19

RC4V19-HA

WHT-BLK 224

BLK-RED 318
815O278O244

10

5

3

KP1A

Cooling

582/444/324

40/33/26

930/760/600

Heating

606/498/396

39/33/26

960/830/700

Electrical

data

Fan

motor

Special

remarks

Capacity

NOTE: 1. Test conditions are based on ISO 5151.

SPECIFICATION

Cooling : Indoor DB27°C WB19°C Heating : Indoor DB20°C

Outdoor DB35°C WB24°C Outdoor DB7°C WB6°C

Indoor-Outdoor piping length : 5m

5

4

90

80

70

60

50

40

30

20

10

63 125 250 500 1000 2000 4000 8000

APPROXIMATE
TERESHOLD OF
HEARING FOR
CONTINUOUS
NOISE

NC-60

NC-50

NC-40

NC-30

NC-20

NC-70

OCTAVE BAND SOUND PRESSURE LEVEL, dB re 0.0002 MICRO BAR

BAND CENTER FREQUENCIES, Hz

Test conditions,

Cooling : DB27: WB19:
Heating : DB20: WB -:

MSC-CB20VB

COOLING

High

FUNCTIONFAN SPEED

36

HEATING

SPL(dB

(A)) LINE

90

80

70

60

50

40

30

20

10

63 125 250 500 1000 2000 4000 8000

APPROXIMATE
TERESHOLD OF
HEARING FOR
CONTINUOUS
NOISE

NC-60

NC-50

NC-40

NC-30

NC-20

NC-70

OCTAVE BAND SOUND PRESSURE LEVEL, dB re 0.0002 MICRO BAR

BAND CENTER FREQUENCIES, Hz

Test conditions.

Cooling : DB27: WB19:
Heating : DB20: WB -:

MSC-CB25VB

COOLING

High

FUNCTIONFAN SPEED

36

HEATING 39

SPL(dB

(A)) LINE

90

80

70

60

50

40

30

20

10

63 125 250 500 1000 2000 4000 8000

APPROXIMATE
TERESHOLD OF
HEARING FOR
CONTINUOUS
NOISE

NC-60

NC-50

NC-40

NC-30

NC-20

NC-70

OCTAVE BAND SOUND PRESSURE LEVEL, dB re 0.0002 MICRO BAR

BAND CENTER FREQUENCIES, Hz

Test conditions.

Cooling : DB27: WB19:
Heating : DB20: WB -:

MSC-CB35VB

COOLING

FUNCTIONFAN SPEED

40

HEATING

High

39

SPL(dB

(A)) LINE

INDOORUNIT

WALL

MICROPHONE

0.8m

1m

NOISE CRITERIA CURVES

6

5

OUTLINES AND DIMENSIONS

MSC-CB20VB
MSC-CB25VB

INDOOR UNIT

278

60

58

162

Wireless remote controller

606

783

815

Installation plate

Indoor unit

149

19

Power supply cord
Lead to right 1.0m
Lead to left 0.3m

81.5

41

81.5

Air in

30

Air out

242 5

7 or more

244

326326

Installation plate

{

90

110

133.5

4.5

271

231.5

42

2.5

81.5

Wall hole

Liquid line
Gas line
Insulation

Drain hose
(Connected part O,D)
Insulation

[65

[6.35-0.5m

[9.52-0.43m

[37 O.D

[21 I.D

[16

[28

Unit: mm

MSC-CB35VB

INDOOR UNIT

278

60

58

162

Wireless remote controller

606

783

815

Installation plate

Indoor unit

149

19

Power supply cord
Lead to right 1.0m
Lead to left 0.3m

41

Air in

30

Air out

7

242

7 or more

244

161.5161.5

326326

5

Installation plate

{

90

110

81.581.5
Wall hole

Liquid line [6.35-0.5m
Gas line
Insulation

Drain hose
(Connected part O,D)
Insulation

17.5

258

218.5

42

2.5

[65

[9.52-0.43m

[37 O.D
[21 I.D

[16

[28

6

SYMBOL

NR11
RT11
RT12

SR141

NAME

NAME NAME
INDOOR FAN CAPACITOR
FUSE(T3.15AL250V)
INDOOR FAN MOTOR (INNER FUSE)
VANE MOTOR

VARISTOR
ROOM TEMPERATURE THERMIST OR
INDOOR COIL THERMISTOR
SOLID STATE RELAY

TERMINAL BLOCK

SYMBOL

C11
F11

MF

MV

SYMBOL

TB

T11

TRANSFORMER

MF

1
2
3
4
5
6

125

CNCN

109

5

REMOTE
CONTROLLER

23

POWER MONITOR
RECEIVER P.C.BOARD

GRN

LD103

PE

12V

FOR
MU OR
MUX TYPE

FOR MUH OR
MXZ-A TYPE

MV

GRN/YLW

POWER
SUPPLY
CORD

~/N 230V

50Hz

TO OUTDOOR
UNIT
CONNECTING

12V

1

2

N

3

L

BRN

BLU

BLK

WHT

BLU

RED

BRN

5

CN
151

1

2

CN202

1

2

3

CN201

LD105

CN211

ELECTRONIC CONTROL P.C. BOARD

F11

T11

NR11

RT11

RT12

CN
112

CN
111

5

3

1

CN
121

BLK
GRY
YLW
BRN

3

WHT
RED

C11

SR141

CIRCUIT BREAKER

TB

WIRING DIAGRAM

MSC-CB20VB MSC-CB25VB MSC-CB35VB

INDOOR UNIT

NOTE:1. About the outdoor side electric wiring refer to the outdoor unit electric wiring diagram for servicing.

2. Use copper conductors only. (For field wiring)

3. Symbols below indicate.

/: Terminal block, : Connector

7

REFRIGERANT SYSTEM DIAGRAM

MSC-CB20VB MSC-CB25VB MSC-CB35VB

INDOOR UNIT

Indoor
heat
exchanger

Room temperature

thermistor
RT11

Refrigerant flow
in cooling

Refrigerant pipe [9.52
(with heat insulator)

Indoor coil
thermistor
RT12

Flared connection

Flared connection

Refrigerant pipe [6.35

(with heat insulator)

8

Unit:mm

8

No. 1 unit
No. 2 unit
No. 3 unit
No. 4 unit

1 unit operation
No modification

–
–
–

2 units operation

Same as at left

Solder J1

–
–

3 units operation

Same as at left
Same as at left

Solder J2

–

4 units operation

Same as at left
Same as at left
Same as at left

Solder both J1 and J2

Slide switch

Type

The position
of the slide
switch

COOL ONLYCOOL & HEAT

SERVICE FUNCTIONS

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB

8-1. TIMER SHORT MODE

For service, set time can be shortened by short circuit of JPG and JPS the electronic control P.C. board.
The time will be shortened as follows. (Refer to 9-6.)

Set time : 1 minute

Set time : 3 minutes ➔ 3-second (It takes 3 minutes for the compressor to start operation. However, the starting time is

8-2. P.C. BOARD MODIFICATION FOR INDIVIDUAL OPERATION

A maximum of 4 indoor units with wireless remote controllers can be used in a room.
In this case, to operate each indoor unit individually by each remote controller, P.C. boards of remote controller must be
modified according to the number of the indoor unit.

How to modify the remote controller P.C. board

Remove batteries before modification. The board has a print as shown below :

➔ 1-second

shortened by short circuit of JPG and JPS.)

Remote controller model : KP1A

The P.C. board has the print “J1” and “J2”. Solder “J1” and “J2” according to the number of indoor unit as shown in Table 1.
After modification, press the RESET button.

J2

J1

NOTE : For remodelling, take out the

batteries and press the
OPERATE/STOP(ON/OFF)
button twice or 3 times at first.
After finish remodelling, put
back the batteries then press
the RESET button.

Table 1

How to set the remote controller exclusively for particular indoor unit

After you turn the breaker ON, the first remote controller that sends the signal to the indoor unit will be regarded as the
remote controller for the indoor unit.
The indoor unit will only accepts the signal from the remote controller that has been assigned to the indoor unit once they
are set.
The setting will be cancelled if the breaker has turned off, or the power supply has shut down.
Please conduct the above setting once again after the power has restored.

8-3. REMOTE CONTROLLER (How to set the type)

This remote controller setting needs to be switched according to the type of air conditioner (COOL & HEAT or COOL
ONLY).
If the setting is incorrect, the air conditioner does not operate normally. Therefore, check if the setting corresponds to the
type of air conditioner. If not, correct the setting as shown below.

9

SW2-1 sets the AUTO RESTART FUNCTION ON / OFF.
SW2-2 switches over the MU & MUX type / MUH & MXZ type.

When the units are shipped from the factory, SW2 is as follows.
SW2-1: AUTO RESTART FUNCTION ON
SW2-2: MUH & MXZ type

}

SW2

FRONT

12

12

IC101

CN151

SW1

CN112

CN121

L101

CN201

F11

CN202

C11

CN211

SW2

LD105

8-4. MU & MUX TYPE / MUH & MXZ TYPE SWITCH OVER AND AUTO RESTART FUNCTION

1 2

1 2

1 2

SW2 SW2

1 2

Outdoor unit

MUH & MXZ type

Set 2 switch downside.

Outdoor unit

MU & MUX type

Set 2 switch upside.

1 2

SW2 SW2

1 2

1 2

1 2

AUTO RESTART

FUNCTION ON

Set 1 switch downside.

AUTO RESTART

FUNCTION OFF

Set 1 switch upside.

1. MU & MUX TYPE / MUH & MXZ TYPE SWITCH OVER

The indoor units for MU & MUX type and MUH & MXZ type
are common specifications. Set switch according to the
type of outdoor unit. The units are set for
MUH & MXZ type when they are shipped from the factory.

How to switch over MU & MUX TYPE / MUH & MXZ TYPE

! Turn off the main power for the unit.
@ Pull out the electronic control P.C. board, and change

switch(SW2-2) on the indoor electronic control P.C. board
according to the type of outdoor unit as following figures.

2. AUTO RESTART FUNCTION

When the indoor unit is controlled with the remote controller, the operation mode, set temperature, and the fan speed
are memorized by the indoor electronic control P.C.board. The “AUTO RESTART FUNCTION” sets to work the moment
power has restored after power failure.Then, the unit will restart automatically. However if the unit is operated in “I
FEEL CONTROL” mode before power failure, the operation is not memorized. In “I FEEL CONTROL” mode, the opera­tion is decided by the initial room temperature. “AUTO RESTART FUNCTION” is ON when the units are shipped from
the factory.

Operation

! If the main power (230V AC) has been cut, the operation settings remain.
@ After the power is restored, the unit restarts automatically according to the memory. (However, it takes at least 3

minutes for the compressor to start running.)

How to release “AUTO RESTART FUNCTION”

! Turn off the main power for the unit.
@ Pull out the electronic control P.C. board, and change switch(SW2-1) on the indoor electronic control P.C. board as

following figures.

NOTE

•The operation settings are memorized when 10 seconds have passed after the remote controller was operated.

•If main power is cut while AUTO START/STOP timer is active, the timer setting is cancelled.

•If the unit has been off with the remote controller before power failure, the auto restart function does not work as the

power button of the remote controller is off.

•To prevent breaker off due to the rush of starting current, systematize other home appliance not to turn on at the same

time.

•When some air conditioners are connected to the same supply system, if they are operated before power failure, the

starting current of all the compressors may flow simultaneously at restart.
Therefore, the special counter-measures are required to prevent the main voltage-drop or the rush of the starting current
by adding system that allows the units to start one by one.

NOTE:•If the indoor-outdoor connecting wire is incorrectly

connected on the terminal block, the unit does not
operate normally.

•If a ground is incorrect, it may cause an electric shock.

10

9

Lead wiring

Housing point

Insert the negative pole
of the batteries first.
Check if the polarity of
the batteries are correct.

HEAT

/FAN

/

RESET button

HEAT
/FAN

/

lighted

flashing

Operation Indicator

TROUBLESHOOTING

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB

9-1. Cautions on troubleshooting

1. Before troubleshooting, check the following:

1) Check the power supply voltage.

2) Check the indoor/outdoor connecting wire for mis-wiring.

2. Take care the following during servicing.

1) Before servicing the air conditioner, be sure to turn off the unit first with the remote controller, and then after confirm­ing the horizontal vane is closed, turn off the breaker and/or disconnect the power plug.

2) Be sure to turn OFF the power supply before removing the front panel, the cabinet, the top panel, and the electronic
control P.C. board.

3) When removing the electronic control P.C. board, hold the edge of the board with care NOT to apply stress on the
components.

4) When connecting or disconnecting the connectors, hold the housing of the connector. DO NOT pull the lead wires.

3. Troubleshooting procedure

1) First, check if the OPERATION INDICATOR lamp on the indoor unit is flashing on and off to indicate an abnormality.
To make sure, check how many times the abnormality indication is flashing on and off before starting service work.

2) If the electronic control P.C. board is supposed to be defective, check the copper foil pattern for disconnection and the
components for bursting and discoloration.

3) When troubleshooting, refer to 9-2. and 9-3.

4. How to replace batteries

Weak batteries may cause the remote controller malfunction.
In this case, replace the batteries to operate the remote controller normally.

1 Remove the front lid and insert batteries.

2 Press the RESET button.

Then reattach the front lid.

NOTE1 : If the RESET button is not pressed, the remote controller may not operate correctly.
NOTE2 : INFORMATION FOR MULTI SYSTEM AIR CONDITIONER

(OUTDOOR UNIT : MXZ-A14WV MXZ-A18WV)

Multi system air conditioner (Outdoor unit MXZ-A14WV MXZ-A18WV) can connect two or more indoor units with one
outdoor unit.

According to the capacity, two or more units can operate simultaneously.

•When you try to operate two or more indoor units with one outdoor unit simultaneously, one for the cooling and the
other for heating, the operation mode of the indoor unit that operates earlier is selected. The other indoor units that
will start the operation later cannot operate, indicating as shown in the figure below. In this case, please set all the
indoor units to the same operation mode.

•When indoor units start the operation while the defrosting of outdoor unit is being done, it takes a few minutes (max.
10 minutes) to blow out the warm air.

•In the heating operation, though indoor unit that does not operate may get warm or the sound of refrigerant flowing

may be heard, they are not malfunction. The reason is that the refrigerant continuously flows into it.

11

9-2. Instruction of troubleshooting

Start

Indoor unit
operates.
Outdoor unit
doesn't
operate.

Indoor unit
doesn't receive
the signal from
remote controller.

Indoor unit
operates.
Outdoor unit
doesn't operate
normally.

OPERATION
INDICATOR
lamp on the
indoor unit is
flashing on
and off.

Outdoor unit
operates in
only Test Run
operation.

Outdoor unit
doesn't
operate
even in
Test Run
operation.

Indoor unit
operates,
when the
EMERGENCY
OPERATION
switch is
pressed.

Indoor unit
doesn't operate,
when the
EMERGENCY
OPERATION
switch is
pressed.

Check room
temperature
thermistor.
Refer to 9-6.
"Test point
diagram and
voltage".

MUH-GA20/GA25/GA35VB
MUX-2A28/2A59/3A60/
3A63/2A70/4A73VB

Refer to
"Check of
outdoor unit".

Refer to 9-5.
B "Check of
remote
controller
and receiver
P.C. board".

MUH-GA20/GA25/GA35VB
MXZ-A14/A18WV

Flash on and off at

0.5-second intervals
Cause:
Indoor/Outdoor unit

• Mis-wiring or
trouble of serial signal

2-time flash
Cause:
Indoor unit

• Trouble of
room temp­ erature/
indoor coil
thermistor

3-time flash
Cause:
Indoor unit

• Trouble of
indoor fan
motor

6-time flash
Cause:
Outdoor unit

• Trouble of
thermistor
in outdoor
unit

7-time flash
Cause:
Outdoor unit

• Trouble of
outdoor
control
system

Check room
temperature
thermistor
and indoor
coil thermis­tor.
Refer to 9-6.
"Test point
diagram and
voltage".

Refer to 9-5.
A "Check of
indoor fan
motor".

4-time flash
Cause:
Indoor unit

• Trouble of
indoor unit
control
system

Replace the
indoor
electronic
control
P.C. board.

MUH-GA20/GA25/GA35VB
MXZ-A14/A18WV

Refer to
"Check of
outdoor
thermistor"
and others.

MUH-GA20/GA25/GA35VB
MXZ-A14/A18WV

Replace the
deicer
P.C. board
and others.

Refer to 9-5. D "How to
check mis-wiring and serial
signal error (When outdoor
unit doesn't work)".
W1

1. Check indoor /
outdoor
connecting wire.

2. Refer to 9-5. C
"Check of indoor
electronic control
P.C. board".

Outdoor unit
doesn't
stop even
if indoor unit
stops.

Unit doesn't
operate
normal
operation in
COOL or
HEAT mode.

MU-GA20/GA25/GA35VB

Check of wiring
diagram of
outdoor unit".

MUH-GA20/GA25/GA35VB

Refer to
"Check of
outdoor unit".

MUH-GA20/GA25/GA35VB
MXZ-A14/A18WV

Refer to
"Check of
R.V. coil" and
others.

W1.<The case of the trouble of the serial signal>
When the power is turned off and then turned on again, the indication shows “the trouble of mis-wiring”.

As for outdoor unit MU type, refer to service manual OB386.
As for outdoor unit MUH type, refer to service manual OB387.
As for outdoor unit MUX type, refer to service manual OB384.
As for outdoor unit MXZ type, refer to service manual OB319.

Indoor unit
operates.
But indoor
unit doesn't
blow out
cool air.

MUX-2A28/2A59/3A60/
3A63/2A70/4A73VB

Refer to
"Check of
indoor/outdoor
units' connection
and outdoor
unit".

10-time flash
Cause:
Outdoor unit

MXZ type

• Outdoor
refrigerant
system
abnormality

MXZ type

Refer to
outdoor
refrigerant
system
related items.

MXZ type

5-time flash
Cause:
Outdoor unit

• Outdoor
power
system
abnormality

Refer to
"Check of
inverter/
compressor"
and "Check
of power
supply".

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB

12

Operation Indicator

· Flashing of the OPERATION INDICATOR lamp (on the left-hand side) indicates possible abnormalities.

· The OPERATION INDICATOR lamp (on the left-hand side) is lighting during normal operation.

flashing

• The following indication does not depend on the shape of lamp.

No.

1

2

5

7

8

SymptomOperation indicator lamp Detection method

Checkpoint

0.5-second ON

0.5-second OFF

MUH or
MXZ type

Mis-wiring
or Serial
signal

MUH or
MXZ type

Defrost
thermistor

MUH or
MXZ type

Outdoor
control
system
error

When the defrost thermistor shorts or opens
after the compressor start-up.

When it cannot properly read data in the non­volatile memory of outdoor electronic control
P.C. board.

When the operation mode of each indoor unit
is differently set to COOL(includes DRY) and
HEAT at same time, the operation mode of
indoor unit that has operated at first has the
priority.

● Check outdoor DEICER P.C.
board and others.

● Check resistance of
thermistor.

● Reconnect connector.
Refer to service manual
OB387 or OB319.

● Check outdoor DEICER P.C.
board and others.

Refer to service manual

OB387 or OB319.

● Unify the operation mode.

● Check switch SW2-2.(MU &

MUX type or MUH & MXZ
type)

● Check wiring (visual check
and conductivity check).

● Check indoor electronic
control P.C.board.

● Check outdoor DEICER P.C.
board and others.

● Check electrical parts.

● Check resistance of

thermistor.

● Reconnect connector.

● Check indoor electronic

control P.C.board.

3

Indoor coil
thermistor

Room
temperature
thermistor

9

MXZ type

Outdoor
refrigerant
system
error

When the compressor operation has been in­terrupted by LEV protection continuously 5
minutes, the compressor stops operation.

Abnormal

point

Outdoor unit
does not run.

Outdoor unit
does not run.

Outdoor unit
does not run.

Outdoor unit
does not run.

Outdoor unit
does not run.

Outdoor unit
does not run.

2-time flash

2.5-second OFF

When serial signal from outdoor unit stops for
4 to 5 seconds.

Detect Indoor coil/room temperature thermis­tor short or open circuit every 8 seconds dur­ing operation.

3-time flash

2.5-second OFF

Indoor fan motor
repeats 12 sec­onds ON and 3
minutes OFF.
When the indoor
fan motor
breaks, the fan
keeps stopping.

When rotational frequency feedback pulse
signal is not emit during 12-second indoor fan
operation.

When the compressor operation is
continuously three times interrupted by over
current protection within 1 minute after start­up , it stops operation.

● Disconnect connector
CN211 and then check
connector CN121 2-3 to
make sure rotational
frequency feedback signal of

1.5V or over exists.

● Check indoor electronic
control P.C. board.

● Check indoor fan motor.

● Reconnect connector.

● Check the inverter output.

● Check the compressor.

Indoor fan
motor

6-time flash

2.5-second OFF

● Refer to "Check of LEV".

● Check refrigerant circuit and

refrigerant amount.

● Check outdoor electronic
control P.C. board.
Refer to service manual
OB319.

6

5-time flash

2.5-second OFF

Operation Indicator

MXZ type

Operation
mode
setting

Lighted

Flashing

Outdoor unit
operates but
indoor unit
does not run.

4

4-time flash

2.5-second OFF

Indoor
control
system

When it cannot properly read data in the
nonvolatile memory of indoor electronic
control P.C. board.

Outdoor unit
does not
operate.

● Replace the indoor electronic
control P.C. board.

7-time flash

2.5-second OFF

10-time flash

2.5-second OFF

MXZ type

Outdoor
power
system

2.5-second OFF

9-3. Troubleshooting check table

❈ Before taking measures, make sure that the symptom reappears, for accurate troubleshooting.
Self check table

13

9-4. Trouble criterion of main parts

RED

BLK

YLW

FUSE

GRY
BRN

WHT

RED

YLW

BRN

ORN

GRN

ROTOR

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB

Part name

Room
temperature
thermistor (RT11)

Indoor coil
thermistor (RT12)

Indoor fan
motor (MF)
INNER FUSE
136i3°C
CUT OFF

Measure the resistance with a tester.
Refer to 9-6. "Test point diagram and voltage", "Indoor electronic control P.C.

board", the chart of thermistor.

Measure the resistance between the terminals with a tester.
(Coil wiring temperature10°C ~ 30°C)

Color of

lead wire

Motor partSensor part

BLK-RED

Measure the voltage Power ON.

Color of

lead wire

BRN-YLW
YLW-GRY

Check method and criterion

Normal

MSC-CB20/CB25VB

271 ~ 295ΩWHT-BLK
180 ~ 196Ω

MSC-CB35VB

215 ~ 233Ω

305 ~ 331Ω

Normal

MSC-CB20/CB25/CB35VB

4.5 ~ 5.5V

(When fan revolved one time)

0V➔5V➔0V

(Approx.)

Figure

Measure the resistance between the terminals with a tester.
(Part temperature10°C ~ 30°C)

Vane motor
(MV)

9-5. Troubleshooting flow

When OPERATION INDICATOR lamp flashes 3-time.

Indoor fan motor doesn’t operate.

AA

Check of indoor fan motor

Turn OFF the power supply.
Check connector CN211 visually.

Reconnect the lead wires.

Disconnect lead wires from connector CN211 on indoor electronic control P.C. board.
Measure resistance between lead wires No.1 and No.5 and then No.3 and No.5.

No

Are lead wires connected?

Is resistance 0 (short circuit) or ∞ (open circuit)?

Repair or replace the indoor fan motor.

Normal

MSC-CB20/CB25/CB35VB

240 ~ 260Ω

Yes

Yes

Yes ( 0 or ∞ )

14

Is soldered point of the

connector correctly soldered?

Turn ON the power supply. Stop it if the unit operates.
Insert screwdriver into air outlet to rotate indoor fan
motor slowly for 1 revolution or over, and measure volt-

No

(others)

age No.2(+) and No.3(-) on CN121.

No

Does voltage repeat 0V DC and 5V DC?

Replace the indoor electronic control P.C. board.

Yes

No

Resolder it.

Indoor unit operates by pressing the EMERGENCY OPERATION switch, but doesn’t operate with the remote controller.

BB

Check of remote controller and receiver P.C. board

wCheck the remote controller is exclusive for this air conditioner.

Switch on the remote controller.

Is LCD display on the remote con­troller displayed?

No
(not clear)

Yes

Remove batteries, then set them back and press the RESET
button. Check if the unit operates with the remote controller.

Does the unit operate with the
remote controller?

No

Turn on a radio to AM and press switch
on the remote controller.

Yes

OK

Measure the voltage between receiver P.C. board connector CN302

(–)

No.3

and No.5

(+)

Replace the power monitor, receiver P.C. board.

Replace the batteries. (Refer to 9-1-4.)

Is noise heard from radio?

Yes

Are there any fluorescent lights of
inverter or rapid-start type within
the range of 1m?

No

when the remote controller button is pressed.

Is the voltage approx. 4V DC?

No(5V or 0V DC)

No

Yes

Yes

Replace the remote controller.

• Reinstall the unit away from lights.

• Attach a filter on receiving part.

Replace the indoor electronic control
P.C. board.

The unit doesn’t operate with the remote controller.
Also, the OPERATION INDICATOR lamp doesn’t light up by pressing the EMERGENCY OPERATION switch.

CC

Check of indoor electronic control P.C. board

Check the both “parts side” and “pattern
side” of indoor electronic control P.C.
board visually.

Turn OFF the power supply.
Remove indoor fan motor connector CN211 and
vane motor connector CN151 from the indoor electronic
control P.C. board and turn ON the power supply.

Does the unit operate with the remote controller?
Does the OPERATION INDICATOR lamp light up
by pressing the EMERGENCY OPERATION switch?

Yes

Turn OFF the
power supply.

Be sure to check both resistances.

Replace the vane
motor.

Yes

Is winding
resistance of
vane motor 0 "?

Is winding
resistance of
fan motor 0 "?

Yes

Replace the fan motor.

No

No

No

Turn OFF the
power supply.

Replace the fuse.

Yes

Is fuse (F11) blown?

Be sure to check both fuse
and varistor in any case.

Is varistor (NR11) burnt?

Yes

Replace the varistor.

No

Replace the indoor
electronic control
P.C. board.

No

15

Serial signal error is indicated.
(0.5-sec. ON, 0.5-sec. OFF)

1. Turn OFF the power supply(indoor / outdoor unit) and disconnect indoor and outdoor connecting wire on indoor side.

2. Short-circuit between indoor terminal block N and 3.

3. Turn ON the power supply(indoor unit) and press once EMERGENCY OPERATION switch.

During EMERGENCY OPERATION,
is there 10V DC between both ends
of R601?
(By tester, the stylus is between 5 ~10V)

Start

Turn OFF the power supply(indoor/outdoor unit).

No

No

Is there 20V DC between both ends of
R132 on indoor electronic control P.C.
board ?
( By tester, the stylus is between 0 ~ 20V. )

•Turn OFF the power supply(indoor unit).

•Connect ON indoor and outdoor connecting wire.

Is the outdoor unit "MUH" type?

•Turn ON the power supply(indoor/outdoor unit).

•Press once EMERGENCY OPERATION switch.

•3 min. later, check the self-check result
displayed on OPERATION INDICATOR
lamp on indoor unit.

w 2

Is this mis-wiring, poor contact,
or disconnection of wire?

Make them sure.

Replace the indoor electronic
control P.C. board.

Turn ON the power supply(outdoor unit).

Is there 230V AC between outdoor terminal
block L-N (TB1)?

No

Check the outdoor power supply,
power supply cord and
connection.

Yes

Turn ON the power supply(indoor unit).

No

Replace the deicer P.C. board.

Yes

No

Make the wiring between CN730
on the deicer P.C. board and
outdoor terminal block correct.

Replace the deicer P.C. board.

Yes

Yes

Yes

Set the switch(SW2-2) on the indoor electronic
control P.C. board to MU or MUX type.

w1

Yes

Does the unit operate?

OK

Yes

No

No

Refer to the
"Instruction of
troubleshooting."

w 2 Short circuit of JPG and JPS on the indoor electronic control
P.C. board enables self-check to be displayed in 3 seconds.

w 1 Set the switch(SW2-2) on indoor electronic control P.C. board to

MU or MUX type, when the outdoor unit is MU or MUX type.
If the setting is MUH or MXZ type, the unit does not work.

Is there 5V DC between J205 + –J101 - on the deicer P.C. board?

As for outdoor unit MUH type, refer to service manual OB387.
As for outdoor unit MXZ type, refer to service manual OB319.

When OPERATION INDICATOR lamp flashes 0.5-second intervals or 1-time.
Outdoor unit does not operate.

DD

How to check mis-wiring and serial signal error

<MUH-CB20/GA25/GA35VB, MXZ-A14/A18/A26/A32WV>

16

Indoor coil thermistor (RT12)
Room temperature thermistor (RT11)

Temperature (:)

Resistance (k")

9-6. Test point diagram and voltage

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB
Indoor electronic control P.C. board

Fuse F11 250V AC 3.15A

Power supply input
230V AC

}

R132

Indoor fan motor
230V AC

}

Safety device of
fan by horizontal
vane CN1R1

Varistor
(NR11)

J12

12V

+

{

DC

–

J33

Power monitor,
receiver P.C. board

J33

+

–

}

5V DC

J23

Room temperature
thermistor RT11

Indoor coil
thermistor
RT12

Timer short mode
point JPG, JPS

}

(Refer to 8-1.)

Emergency
operation switch

SW2

(Refer to 8-4.)

1sets the Auto restart

function ON/OFF.

2switches over MU&MUX type/

MUH & MXZ type.

CN302

17

10

(1) Slide the sleeve and check if there is a locking lever or not. (2) The terminal with this connector has the locking

mechanism.

1Slide the sleeve.
2Pull the terminal while

pushing the locking
lever.

1Hold the sleeve, and
pull out the terminal
slowly.

The terminal which has the locking mechanism can be detached as shown below.
There are two types ( Refer to (1) and (2)) of the terminal with locking mechanism.
The terminal without locking mechanism can be detached by pulling it out.
Check the shape of the terminal before detaching.

<"Terminal with locking mechanism" Detaching points>

Connector

Sleeve

Locking lever

DISASSEMBLY INSTRUCTIONS

MSC-CB20VB MSC-CB25VB MSC-CB35VB
INDOOR UNIT

OPERATING PROCEDURE PHOTOS

1. Removing the front panel

(1) Remove the screw caps of the front panel.

Remove the screws.

(2) Pull the panel down to your side slightly and unhook the

catches at the top.

2. Removing the electronic control P.C. board and the
power monitor, receiver P.C. board

NOTE : In case of removing only indoor electronic control

P.C. board, work (3) is not necessary.
(1) Remove the front panel. (Refer to 1.)
(2) Remove the power monitor, receiver P.C. board holder

from the bottom of electrical box.

(3) Open the power monitor, receiver P.C. board holder and

remove the power monitor, receiver P.C. board.

(4) Remove the screw of the electrical cover and the electrical

cover.
(5) Remove the screw of the V.A. clamp and the V.A. clamp.
(6) Remove the screw of the cord clamp and the cord clamp.
(7) Remove the screw of the terminal block.
(8) Remove the screw of the ground wire.
(9) Pull out indoor electronic control P.C. board slightly.
(10)

Disconnect all (except CN109 and CN125) the connectors

on the electronic control P.C. board.
(11)

Remove the electronic control P.C. board.

(12)

Disconnect the connector of power monitor, receiver P.C.

board (CN109) on the electronic control P.C. board.

Photo 1

Screws of the front panel

Photo 2

Screw of the
ground wire

Power monitor, receiver
P.C. board holder

Terminal block
fixing screw

Indoor electronic
control P.C. board

Cord clamp fixing
screw

Screw of the V.A.
clamp

Screw of the
electrical cover

18

OPERATING PROCEDURE

3. Removing the electrical box

(1) Remove the front panel. (Refer to 1.)
(2) Remove the electrical cover. (Refer to 2.)
(3) Remove the V.A. clamp. (Refer to 2.)
(4) Remove the cord clamp. (Refer to 2.)
(5) Remove the terminal block. (Refer to 2.)
(6) Remove the screw of ground wire. (Refer to 2.)
(7) Disconnect the connector of the indoor coil thermistor

(CN112), the fan motor connector (CN211 and CN121) and
the vane motor connector (CN151) on the electronic con­trol P.C. board.

(8) Remove the fan motor lead wire and indoor coil thermistor

from the electrical box.

(9) Remove the lead wire of vane motor from the bottom of

electrical box.

(10)

Remove the screw fixing the electrical box, remove the

electrical box.

Photo 3

PHOTOS

Indoor coil thermistor
connector

Fan motor connector

Vane motor
connector

Screw of the
electrical box

4. Removing the nozzle assembly and the vane motor

(1) Remove the front panel. (Refer to 1.)
(2) Remove the electrical box. (Refer to 3.)
(3) Pull out the drain hose from the nozzle assembly, remove

the nozzle assembly.

(4) Remove the screws of the vane motor, disconnect the

vane motor connector.

(5) Remove the vane motor.

5. Removing the indoor fan motor and the line flow fan

(1) Remove the front panel. (Refer to 1.)
(2) Remove the electrical box. (Refer to 3.)
(3) Pull out the drain hose from the nozzle assembly, remove

the nozzle assembly. (Refer to 4.)
(4) Remove the screw of the lead cover and lead cover.
(5) Release the hooks to open the motor band slightly.
(6) Loosen the hexagon socket set screw from the line flow

fan.
(7) Remove the screws fixing the motor bed, remove the fan

motor with motor band and the motor bed.
(8) Remove the screws fixing the left side of the heat

exchanger.
(9) Lift the left side of the heat exchanger.
(10)

Remove the line flow fan.

Photo 6

Hexagon socket set screw

Photo 4

Drain hose

Photo 5

Screws of the
left side of the
heat exchanger

Photo 7

Screws of the vane motor

Screw of
the lead
cover

Hooks of the
motor band

Screws of
the motor
bed

19

11

1
2

3
4
5

6
7
8

E02 763 234
E02 764 234
E02 A59 000
E02 763 067
E02 A59 010
E02 408 142
E02 763 100
E02 764 100
E02 763 975
E02 408 970
E02 751 970

BOX
BOX
PANEL ASSEMBLY
SCREW CAP
FRONT PANEL
CATCH
CATECHIN AIR FIL TER
CATECHIN AIR FIL TER
CORNER BOX (RIGHT)
INSTALLATION PLATE
INSTALLATION PLATE

Symbol

in Wiring

Diagram

Q'ty/unit

1

1
2
1
2
2

1
1

Including No.3,4,5
2PCS/SET

2PCS/SET

Remarks

Part No.

No.

Part Name

MSC-CB20VB-

E1

1
1
2
1
2

2
1

1

1

1
2
1
2
2

1
1

1
1

1
1

1
1

E02 749 426
E02 527 083

9

10

REMOTE CONTROLLER
REMOTE CONTROLLER HOLDER

MSC-CB25VB-

E1

MSC-CB35VB-

E1

KP1A

PARTS LIST

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB

11-1. INDOOR UNIT STRUCTURAL PARTS

1 (W)

2

3

4

5

6 (W)

11-1. INDOOR UNIT STRUCTURAL PARTS

8 (W)

7

Optional parts

(See 12.)

(W) These figures show about MSC-CB35VB.

11-2. ACCESSORY AND

REMOTE CONTROLLER

9

10

11-2. ACCESSORY AND REMOTE CONTROLLER

20

MSC-CB20VB
MSC-CB25VB
MSC-CB35VB

11-3. INDOOR UNIT ELECTRICAL PARTS

11-4. INDOOR UNIT HEAT EXCHANGER

AND FUNCTIONAL PARTS

18

17

16

15

14

1
3

4

2

12

13

11

21
22

5

10

9

6

8

7

(W) This figure shows MSC-CB35VB.

11-3. INDOOR UNIT ELECTRICAL PARTS AND FUNCTIONAL PARTS

Part number that is circled is not shown in the illustration.

Q'ty/unit

MSC-CB25VB-

E1

1
1
1
1
1
1
1
1
1

1

1
1
1
1
1

1
1
1

1

Part No.

No.

E02 001 504

1

E02 661 702

2

E02 A59 235

3

E02 781 040

4

E02 781 041

5

E02 A49 382

6

E02 829 385

7

E02 763 034

8

E02 815 468

9

E02 962 452
E02 963 452

10

E02 964 452
E02 749 303

11

E02 151 308

12

E02 749 333

13

E02 691 375

14

E02 749 300

15

E02 751 300
E02 749 307

16
17

E02 A59 302
E02 408 509

18

E02 751 509
E02 749 385

19

Symbol

Part Name

SLEEVE BEARING
DRAIN HOSE
NOZZLE ASSEMBL Y
VANE UPPER
VANE LOWER
FUSE
VARISTOR
VANE CRANK SET
POWER MONITOR, RECEIVER P.C. BOARD
ELECTRONIC CONTROL P.C.BOARD
ELECTRONIC CONTROL P.C.BOARD
ELECTRONIC CONTROL P.C.BOARD
VANE MOTOR
ROOM TEMPERATURE THERMISTOR
MOTOR BAND
TERMINAL BLOCK
INDOOR FAN MOTOR(RC4V19- )
INDOOR FAN MOTOR(RC4V19- )
INDOOR COIL THERMISTOR
LINE FLOW FAN
BEARING MOUNT
BEARING MOUNT
VARISTOR

in Wiring

Diagram

F11

NR11

MV

RT11

TB
MF
MF

RT12

NR12

MSC-CB20VB-

E1

1
1
1
1
1
1
1
1
1
1

1
1
1
1
1

1
1
1

1

20 (W)

MSC-CB35VB-

E1

1
1
1
1
1
1
1
1
1

1
1
1
1
1

1
1
1

1
1

Remarks

3.15AL250V

AUTO RESTART
AUTO RESTART
AUTO RESTART

3P

Including fan motor rubber
mount 2PCS/SET

Including fan motor rubber
mount 2PCS/SET

11-4. INDOOR UNIT HEAT EXCHANGER

E02 A59 620

20

E02 A61 620

21

E02 151 666

22

E02 151 667

INDOOR HEAT EXCHANGER
INDOOR HEAT EXCHANGER
UNION(GAS)
UNION(LIQUID)

21

1

1
1

1

1
1

1
1
1

{9.52
{6.35

12

Air cleaning filter
(White bellows type)

Model

Part No.

MAC-1300FT

MSC-CB20VB­MSC-CB25VB­MSC-CB35VB-

E1
E1

E1

OPTIONAL PARTS

AIR CLEANING FILTER

● AIR CLEANING FILTER removes fine dust of 0.01 micron from air by means of static electricity.

● Normal life of AIR CLEANING FILTER is 4 months. However, when it becomes dirty, replace it as soon as possible.

● Clogged AIR CLEANING FILTER may reduce the air conditioner capacity or cause frost on the air outlet.

● DO NOT reuse AIR CLEANING FILTER even if it is washed.

● DO NOT remove or attach AIR CLEANING FILTER during unit operation.

22

23

HEAD OFFICE: TOKYO BLDG, 2-7-3, MARUNOUCHI, CHIYODAKU, TOKYO 100-8310, JAPAN

CC

Copyright 2005 MITSUBISHI ELECTRIC ENGINEERING CO.,LTD
Distributed in Dec. 2005. No.OB439 6
Made in Japan

New publication, effective Dec. 2005
Specifications subject to change without notice.