Mitsubishi MSH-GD-VB – E, MU-GD-VB – E, MS-GE-VB – E, MUH-GD-VB – E, MSH-GE-VB – E Service Technical Manual

SERVICE TECHNICAL GUIDE

CONTENTS

1. MSC/MS/MSH MICROPROCESSOR CONTROL · 4

2. MSZ/MLZ MICROPROCESSOR CONTROL ·······11

SPLIT-TYPE AIR CONDITIONERS

No. OBT17

REVISED EDITION-D

Revision D:

•MSC-GE·VB-E, MS-GE·VB-E, MSH­GE·VB-E, MUZ-FD50VA -E, MSZ-GE42/
50VA -

E

and MSZ-CGE42/50VA -E have

been added.

Please void OBT17 REVISED EDITION-C.

CONFIDENTIAL
(FOR INTERNAL USE ONLY)

Models

MSC-GE•VB -

E

MS-GD•VB -

E

· MU-GD•VB -

E

MS-GE•VB -

E

· MU-GE•VB -

E

MSH-GD•VB -

E

· MUH-GD•VB -

E

MSH-GE•VB -

E

· MUH-GE•VB -

E

MSZ-GC•VA -

E

· MUZ-GC•VA(H) -

E

MSZ-HC•VA(B) -

E

· MUZ-HC•VA(B) -

E

MSZ-CHC•VA -

E

MSZ-FD•VA(S) -

E

· MUZ-FD•VA(H)(BH) -

E

MSZ-GE•VA -

E

· MUZ-GE•VA(H) -

E

MSZ-CGE•VA -

E

MLZ-KA•VA -

E

2

Revision A:

• MSZ-FD•VA -

E

has been added.

Revision B:

•MS-GD•VB -E and MSH-GD•VB -E have been added.

Revision C:

• MSZ-FD50VA -

E

, MSZ-GE•VA -E, MSZ-CHC•VA -

E

and MSZ-CGE•VA -E have been added.

Revision D:

• MSC-GE·VB-E, MS-GE·VB-E, MSH-GE·VB-E, MUZ-FD50VA -E, MSZ-GE42/50VA -

E

and MSZ-CGE42/50VA -E

have been added.

3

2. MSZ/MLZ MICROPROCESSOR CONTROL······································································································11

Indoor unit models Outdoor unit models

MSZ-GC22/25/35VA MUZ-GC25/35VA(H)
MSZ-HC25VA MSZ-HC35VA(B) MUZ-HC25VA MUZ-HC35VA(B)
MSZ-CHC25/35VA
MSZ-FD25/35/50VA(S) MUZ-FD25/35VA(H)(BH) MUZ-FD50VABH
MSZ-GE22/25/35/42/50VA MUZ-GE25/35/42/50VA(H)
MSZ-CGE22/25/35/42/50VA
MLZ-KA25/35/50VA

2-1. COOL OPERATION ··································································································································· 11
2-2. DRY OPERATION ······································································································································12
2-3. HEAT OPERATION ····································································································································12
2-4. AUTO CHANGE OVER ··· AUTO MODE OPERATION·············································································15
2-5. OUTDOOR FAN MOTOR CONTROL ········································································································15
2-6. AUTO VANE OPERATION ·························································································································15
2-7. DRAIN PUMP/FLOAT SENSOR CONTROL ·····························································································16
2-8. INVERTER SYSTEM CONTROL ···············································································································17
2-9. OPERATIONAL FREQUENCY CONTROL OF OUTDOOR UNIT ····························································20
2-10. PRE-HEAT CONTROL ·····························································································································21
2-11. EXPANSION VALVE CONTROL/LEV CONTROL ···················································································22

NOTE: As for the multi system type models or MU/MUH-GA type models, refer to the appropriate service technical

guide as well as this service technical guide.

1. MSC/MS/MSH MICROPROCESSOR CONTROL· ·······························································································4

Indoor unit models Outdoor unit models

MSC-GE20VB
MSC-GE25VB
MSC-GE35VB
MS-GD80VB MU-GD80VB
MS-GE50VB MU-GE50VB
MSH-GD80VB MUH-GD80VB
MSH-GE50VB MUH-GE50VB

1-1. COOL OPERATION ·····································································································································4
1-2. DRY OPERATION ········································································································································5
1-3. HEAT OPERATION ······································································································································5
1-4. INDOOR FAN MOTOR CONTROL ··············································································································8
1-5. AUTO VANE OPERATION ···························································································································8
1-6. EXPANSION VALVE CONTROL (LEV CONTROL) ·················································································· 10

4

2. Indoor fan speed control

Indoor fan operates at the set speed by FAN SPEED CONTROL button.

In AUTO the fan speed is as follows.

Initial temperature difference Fan Speed

Room temperature minus set temperature: 1.7°C or more

························································High

Room temperature minus set temperature: between 1 and 1.7°

C ·············································Med.

Room temperature minus set temperature: less than 1°

C ·························································Low

1°C 1.7°C

3°C

3. Coil frost prevention

Temperature control

The coil frost prevention mode in the temperature control is that the indoor fan operates at the set speed and the com-

pressor stops for 5 minutes or more.

Model

Coil frost prevention

ON OFF

Indoor coil thermistor (°C) Indoor coil thermistor (°C)

MSC-GE20VB
MSC-GE25VB

4 °C or less More than 4 °C

MSC-GE35VB 0 °C or less More than 0 °C
MS-GD80VB -1 °C or less More than -1 °C
MS-GE50VB 3 °C or less More than 3 °C
MSH-GD80VB

MSH-GE50VB

1 °C or less More than 1 °C

The coil frost prevention doesn't work for 5 minutes since the compressor has started.

Compressor
Outdoor fan

OFF

ON

(Continuously at set speed)

Indoor fan

ON

ON

OFF

Operation chart
Example

5. Discharge temperature protection (MU-GD80VB, MUH-GD80VB)

The compressor is controlled by the temperature of discharge temperature thermistor for excess rise protection of compres­sor discharge pressure.

• Compressor
When the temperature of discharge temperature thermistor goes to 120°C or more, the compressor is turned OFF. After 3
minutes since the compressor has been turned OFF, if the temperature of discharge temperature thermistor becomes 100
°C or less, the compressor is turned ON.

4. Outdoor fan speed control (MU-GD80VB, MUH-GD80VB)

Outdoor fan speed control is as follows.

Outdoor
fan speed

High
or
Med.

Indoor
fan speed

20°C 22°C

Low

30°C 33°C

High

Temperature of
ambient temperature
thermistor

Low

High
Low

1-1. COOL ( ) OPERATION

1

MSC/MS/MSH MICROPROCESSOR CONTROL

Time control

When the three conditions as follows have been satisfied for 1 hour and 45 minutes, compressor stops for 3 minutes.
a. Compressor has been continuously operating.
b. Indoor fan speed is Low or Med.
c. Room temperature is 26°C or less.
When compressor stops, the accumulated time is cancelled and when compressor restarts, time counting starts from the
beginning.
Time counting also stops temporarily when the indoor fan speed becomes High or the room temperature exceeds 26°C.
However, when two of the above conditions (b. and c.) are satisfied again. Time accumulation is resumed.

-0.3°C

0.3°C

1. Thermostat control (MSC-GE20/25/35VB)
Thermostat is ON or OFF by difference between room temperature and set temperature

Initial temperature difference Thermostat

Room temperature minus set temperature : 0.3°C or more················································ON
Room temperature minus set temperature : less than -0.3°C············································OFF

Set temperature

Difference between room
temperature and set tem­perature during operation

Difference between room
temperature and set tem­perature during operation

5

2. Indoor fan speed control

Indoor fan operates at the set speed by FAN SPEED CONTROL button.
In Auto fan speed becomes Low.

3. The operation of the compressor and indoor/outdoor fan
Compressor operates by room temperature control and time control.
Set temperature is controlled to fall 2°C from initial room temperature.
Indoor fan and outdoor fan operate in the same cycle as the compressor.

● When the room temperature is 23°C or over:
When the thermostat is ON, the compressor repeats 8 minutes ON and 3 minutes OFF.
When the thermostat is OFF, the compressor repeats 4 minutes OFF and 1 minute ON.

● When the room temperature is under 23°C.
When the thermostat is ON, the compressor repeats 2 minutes ON and 3 minutes OFF.
When the thermostat is OFF, the compressor repeats 4 minutes OFF and 1 minute ON.

Set temperature is as shown on the right chart.
The system for dry operation uses the same refrigerant circuit as the
cooling circuit.
The compressor and the indoor fan are controlled by the room tem­perature.
By such controls, indoor flow amounts will be reduced in order to
lower humidity without much room temperature decrease.

DRY operation will not work when the room temperature is 13°C or
below.

1-2. DRY ( ) OPERATION

35

30

25

20

15

10

10 15 20 25 30 35

Set temperature

Initial room temperature

Set temperature and
initial room temperature in DRY mode

Thermostat

Indoor fan

Outdoor fan
Compressor

ON

8 minutes

3

minutes

ON

OFFOFF

OFF

OFF

OFF

OFF

OFF

OFF

ON

ON

ON

ON

ON

ON

Operation time chart
Example
When the room temperature is 23°C or over:

4. Coil frost prevention

• The operation is the same as coil frost prevention during COOL mode.

• The indoor fan operates at the set speed and the compressor does not operate for 5 minutes because the coil frost pre­vention has priority.

1

minute

4

minutes

-0.3°C

0.3°C

1. Thermostat control (MSC-GE20/25/35VB)
Thermostat is ON or OFF by difference between room temperature and set temperature.

Initial temperature difference Thermostat

Room temperature minus set temperature : 0.3°C or more················································ON
Room temperature minus set temperature : less than -0.3°C············································OFF

Set temperature

Difference between room
temperature and set tem­perature during operation

-0.3°C

0.3°C

Set temperature

Difference between room
temperature and set tem­perature during operation

1. Thermostat control (MSC-GE20/25/35VB)
Thermostat is ON or OFF by difference between room temperature and set temperature.

Initial temperature difference Thermostat

Room temperature minus set temperature : less than -0.3°C··············································ON
Room temperature minus set temperature : 0.3°C or more·················································OFF

1-3. HEAT ( ) OPERATION (MSC-GE20/25/35VB, MSH-GD80VB, MSH-GE50VB)

6

(3) Warm air control

When compressor starts in heating operation or after defrosting, the fan changes the speed due to the indoor coil ther­mistor temperature to blow out warm air.
After releasing of cold air prevention, when the indoor coil thermistor temperature is 37°C or above, the fan speed shifts
to the set speed, and when the fan speed is changed by the remote controller, the fan speed is the set speed.
When the indoor coil thermistor temperature is less than 37°C, the fan speed is controlled by time as below.
<Time condition> <Indoor fan speed>
Less than 2 minutes ·······················Low
2 minutes to 4 minutes ···················Med.
4 minutes or more ··························High
The upper limit of the fan speed in MANUAL is the set speed.
The upper limit of the fan speed in AUTO is the speed decided by the indoor fan speed control. (Refer to 1-3.2.(1).)
If the thermostat turns OFF, this operation changes to flow soft control. (MSH-GD80VB, MSH-GE50VB)

(4) Flow soft control (MSH-GD80VB, MSH-GE50VB)

After the thermostat turns OFF, the indoor fan operates at Very Low.
NOTE: When the thermostat turns ON, the fan operates at the set speed. Due to the cold air prevention control, the fan

does not start at set speed until the indoor coil thermistor reads 22°C or more.

3. Outdoor fan speed control (MUH-GD80VB)

Outdoor fan speed control is as follows.

13°C 18°C

Outdoor
fan speed

High

Low

T

emperature of
ambient temperature
thermistor

(2) Cold air prevention control

When the compressor is not operating (MSC-GE20/25/35VB):
( ) If the temperature of indoor coil thermistor RT12 is 0°C or less, the fan stops.
( ) If the temperature of indoor coil thermistor RT12 is more than 0°C, the fan operates at Very Low.

When the compressor is operating:
( ) If the temperature of RT12 is 22°C or more, the fan operates at set speed.
( ) If the temperature of RT12 is less than 22°C and
( ) if the temperature of room temperature thermistor RT11 is 15°C or less, the fan stops.
( ) if the temperature of room temperature thermistor RT11 is more than 15°C, the fan operates at Very Low.

NOTE : If the temperature of RT12 reads from 18°C to 22°C at the air conditioner stating and also after defrosting, this

control works.

Released

Cold Air Prevention

18°C 22°C

Fan speed
Set speed

Very Low or stop

(MSH-GD80VB, MSH-GE50VB) Initial temperature difference Fan speed

Set temperature minus room temperature: 2°C or more ·····················································High
Set temperature minus room temperature: between 1 and 2°C········································· Med.
Set temperature minus room temperature: less than 1°C ····················································Low

1°C 1.7°C

4°C

2°C

2. Indoor fan speed control

(1) In AUTO the fan speed
(MSC-GE20/25/35VB)
Indoor fan speed at set speed by FAN SPEED CONTROL button.

Initial temperature difference Fan speed

Set temperature minus room temperature: 1.7°C or more ·················································High
Set temperature minus room temperature: between 1 and 1.7°

C ·································

Med.

Set temperature minus room temperature: less than 1°

C ·············································

Low

1°C

1.7°C

3°C

Difference between room
temperature and set tem­perature during operation

Difference between room
temperature and set tem­perature during operation

7

4. High pressure protection (MUH-GD80VB, MUH-GE50VB)

During heating operation, the outdoor fan and the compressor are controlled by the temperature of indoor coil thermistor
for excess rise protection of compressor discharge pressure.

• Outdoor fan
When the temperature of indoor coil thermistor goes to 55°C or more, the outdoor fan is turned OFF.
When the temperature of indoor coil thermistor becomes 52°C or less, the outdoor fan is turned ON.

• Compressor
When the temperature of indoor coil thermistor goes to 75°C or more, the compressor is turned OFF.
3 minutes after the compressor is turned OFF and if the temperature of indoor coil thermistor becomes 75°C or less, the

compressor is turned ON.

NOTE: During the high pressure protection and for 10 seconds after high pressure protection, defrosting of outdoor heat

exchanger is not detected by the defrost thermistor.

5. Defrosting

Defrosting of outdoor heat exchanger is controlled by deicer P.C. board, with detection by the defrost thermistor.
(1) Starting conditions of defrost
When all conditions of a) ~ c) are satisfied, the defrosting operation starts.

a) Under the heat operation, the compressor cumulative operation time exceeds 40 minutes without the defrosting opera-

tion working.
b) The defrost thermistor reads -3°C or less.
c) After releasing the high pressure protection 4 minutes and 10 seconds have elapsed.

(2) Releasing conditions of defrost
When the condition d) or e) is satisfied, the defrosting operation stops.

d) The defrost thermistor reads 10°C (MUH-GE50VB) /13°C or more (MUH-GD80VB).
e) The defrosting time exceeds 10 minutes.

(3) Defrosting time chart

Defrost thermistor
13°C or more (MUH-GD80VB)
10°C or more (MUH-GE50VB)

-3°C or less
Outdoor 52C

contactor
(Compressor)

X62
(R.V. coil)

SR61
Outdoor fan

Defrost
counter

Indoor fan

Indoor vane

ON
OFF

ON
OFF

ON
OFF

ON
OFF

ON

OFF
Horizontal

Set position

Maximum 10 minutes

30 seconds

15 seconds

30 seconds

5 seconds

NOTE

Very Low

NOTE: • When the indoor coil thermistor reads above 18°C, indoor fan operates at Very Low for 30 seconds.

• When the indoor coil thermistor reads 18°C or less, the indoor fan stops.

8

1-4. INDOOR FAN MOTOR CONTROL

(1) Rotational frequency feedback control
The indoor fan motor is equipped with a rotational frequency sensor, and outputs signal to the microprocessor to feed-

back the rotational frequency. Comparing the current rotational frequency with the target rotational frequency (High,
Med., Low), the microprocessor controls SR141 and adjusts fan motor electric current to make the current rotational
frequency close to the target rotational frequency. With this control, when the fan speed is switched, the rotational fre­quency changes smoothly.

High

Rotational frequency

High

time

Med.

Low

(2) Fan motor lock-up protection

When the rotational frequency feedback signal has not output for 12 seconds, (or when the microprocessor cannot
detect the signal for 12 seconds) the fan motor is regarded locked-up. Then the electric current to the fan motor is shut­off. 3 minutes later, the electric current is applied to the fan motor again. During the fan motor lock-up, the OPERATION
INDICATOR lamp flashes ON and OFF to show the fan motor abnormality.

1-5. AUTO VANE OPERATION (MSC, MSH)

1. Horizontal vane

(1) Cold air prevention in HEAT operation
When any of the following conditions occur in HEAT operation, the vane angle changes to Angle 1 automatically to pre-

vent cold air blowing on users.
Compressor is not operating.
Defrosting is performed.
Indoor coil thermistor reads 24°C or below.
Indoor coil thermistor temperature is rising from 24°C or below until it reaches 28°C.

NOTE1: If the temperature of the indoor coil thermistor reads from 24 to 28°C at the air conditioner starting, this control

works.

NOTE2: When 2 or more indoor units are operated with multi outdoor unit, even if any indoor unit turns thermostat OFF, this

control doesn’t work in the indoor unit.

Released

Cold Air Prevention

24°C 28°C

Angle 1

Horizontal vane

Set position

Indoor coil thermistor temperature