Mitsubishi Electric MSC-GE-VB Quick start guide

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, MSH-
GE·VB- E, MUZ-FD50VA - E, MSZ-GE42/
50VA - Eand MSZ-CGE42/50VA - Ehave
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 - Ehas been added.
Revision B:
•MS-GD•VB - Eand MSH-GD•VB - Ehave been added.
Revision C:
• MSZ-FD50VA - E, MSZ-GE•VA - E, MSZ-CHC•VA - Eand MSZ-CGE•VA - Ehave been added.
Revision D:
• MSC-GE·VB- E, MS-GE·VB- E, MSH-GE·VB- E, MUZ-FD50VA - E, MSZ-GE42/50VA - Eand 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 compres-
sor 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
1MSC/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 tem-
perature during operation
Difference between room
temperature and set tem-
perature 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 tem-
perature.
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
1010 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 pre-
vention 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 tem-
perature during operation
-0.3°C0.3°C
Set temperature
Difference between room
temperature and set tem-
perature 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)

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(3) Warm air control
When compressor starts in heating operation or after defrosting, the fan changes the speed due to the indoor coil ther-
mistor 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
Temperature 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 tem-
perature during operation
Difference between room
temperature and set tem-
perature 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 fre-
quency 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 shut-
off. 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

9
(2) ECONO COOL ( ) operation (ECONOmical operation)
When ECONO COOL button is pressed in COOL mode, set temperature is automatically set 2°C higher.
Also the horizontal vane swings in various cycle according to the temperature of indoor heat exchanger (Tp( 1)).
SWING operation makes you feel cooler than set temperature. So, even though the set temperature is higher, the air
conditioner can keep comfort. As a result, energy can be saved.
ECONO COOL operation is cancelled when ECONO COOL button, VANE CONTROL button, VANE button or LONG but-
ton is pressed or changed to other operation mode.
NOTE: ECONO COOL operation does not work in COOL mode of “I FEEL CONTROL”.
<SWING operation>
1 Tp: • Value of indoor coil thermistor (MSC-GE20/25/35VB, MS-GE50VB, MSH-GE50VB)
• Average value of indoor coil thermistor (main) and indoor coil thermistor (sub) (MS-GD80VB, MSH-GD80VB)
In swing operation of ECONO COOL operation mode, the initial airflow direction is adjusted to “Horizontal”.
According to the temperature of indoor coil thermistor Tp(1) at starting of this operation, next downward blow time is
decided. Then when the downward blow has been finished, next horizontal blow time is decided.
For initial 10 minutes the swing operation is performed in table G~H for quick cooling.
Also, after 10 minutes when the difference between set temperature and room temperature is more than 2°C, the swing
operation is performed in table D ~ H for more cooling.
The air conditioner repeats the swing operation in various cycle as follows.
Temperature of Tp( 1) Downward blow time
(second) Horizontal blow time (second)
A15°C or less 2 23
B15 to 17°C 5 20
C17 to 18°C 8 17
D18 to 20°C 11 14
E20 to 21°C 14 11
F21 to 22°C 17 8
G22 to 24°C 20 5
HMore than 24°C 23 2

10
NOTE : Opening increases and decreases to be in the target discharge temperature during operation.
Opening
completely
Positioning
Power ON
Initial opening
Standard opening
Remote
controller
ON
Operation Thermostat OFF Standard opening
Thermostat
ON
Opening in stop
Operation
Opening in stop
Remote
controller
OFF
Opening
completely Remote
controller
ON
Positioning
Standard opening
Operation
Time
LEV opening
Initial opening Initial opening
Open
Close
(2) LEV time chart
1-6. EXPANSION VALVE CONTROL (LEV CONTROL) (MU-GD80VB, MUH-GD80VB)
LEV (Expansion valve) is controlled by “Thermostat ON” commands given from the unit.
Standard
specification
Control range Minimum: 54 pulse, Maximum: 500 pulse
Drive speed 30 ~ 90 pulse/second
Opening set The setting is always in opening direction.
(To close LEV, it is closed to the pulse smaller than the one set finally.
Then LEV is opened to the final setting pulse.)
General operation
Stop of indoor unit Opening in stop: 150 pulse →LEV opening is set to become 500 pulse after 3 min-
utes.
Remote controller ON LEV positioning (LEV is closed completely at once)
Power ON (Breaker ON) LEV is positioned. However, afterwards, LEV is not positioned when the remote
controller is turned ON for the first time after the power ON.
Approximately for 2 minutes after
compressor has started. Opening is set by the initial opening. (Initial opening is set according to each operation mode and outer temperature con-
ditions.)
Approximately 2 to 13 minutes (for
11 minutes) after compressor has
started. Opening is set by standard opening.
(Standard opening is set according to each operation mode and outer temperature
conditions.)
13 minutes after compressor has
started. LEV opening is corrected once every 2 minutes so that discharge temperature
becomes the target discharge temperature.
(When the discharge temperature is lower than the target temperature: LEV is cor-
rected in closed direction, when the discharge temperature is higher than the target
temperature: LEV is corrected in opening direction.)
Thermostat OFF Opening in stop: 150 pulse →LEV is set to the initial opening after about 3 minutes.
Thermostat ON Same as the starting of compressor operation
Remote controller OFF Opening in stop: 150 pulse →LEV is set so that the opening is opened completely
at the speed of 4 pulse every 5 seconds in opening after about 3 minutes.
Operation mode Target discharge temperature (°C)
HEAT (MUH-GD80VB) 85
COOL (Normal) 80
COOL (∆RT is less than 2°C, or ∆RT is 2°C or more and less than 3°C.) 70
COOL (∆RT is 3°C or more.) 65
NOTE: When the discharge temperature is 50°C or less on the cool operation, or is 49°C or less on heat operation
(MUH-GD80VB), LEV opening is set in 54 pulse.
When this state continues for 20 minutes, the compressor is stopped and restarts in 3 minutes.
When the compressor is stopped, the indoor unit indicates the abnormality of refrigerant system and stops.
(OPERATION INDICATOR lamp is 10-time flashing ON and OFF.)
(1) Control data
Reference value of target discharge temperature