Mitsubishi Electric MSC-CA20VB Service Technical Manual page 30

(2) Cold air prevention control
The fan runs at set speed when the indoor coil thermistor RT12 temperature exceeds 22°C. The fan operates Low when
the temperature of indoor coil thermistor RT12 is below 18°C. But the fan stops when the indoor fan operates at Very
Low and the room temperature is 15°C or less.
Indoor coil thermistor
RT12 temperature
NOTE : If the temperature of RT12 reads from 18°C to 22°C at the air conditioner starting and also after defrosting, this
control works.
(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 RT12 temperature to blow out warm air.
After releasing of cold air prevention, when the indoor coil thermistor RT12 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 RT12 temperature is less than 37°C, the fan speed is controlled by time as below.
<Time condition>
less than 2 minutes ························Low
2 minutes to 4 minutes···················Med.
4 minutes or more ··························High
The upper limit of the fan speed is the set speed.
If the thermostat turns off, this operation changes to flow soft control.
(4) Flow soft control
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 RT12 reads 22°C or more.
2. Outdoor fan speed control <MUH-GA80VB>
Outdoor fan speed is controlled according to the temperature of ambient temperature thermistor RT63.
Outdoor fan Low operation : Until the outside temperature decreases to 13°C.
Outdoor fan High operation :When the outside temperature decreases to 13°C or less.
3. High pressure protection
<MUH-GA50/60VB>
During heating operation, the outdoor fan motor is controlled by the temperature of indoor coil thermistor RT12 for excess
rise protection of compressor discharge pressure.
(MUH-GA50VB) Outdoor fan OFF
Outdoor fan ON
(MUH-GA60VB) Outdoor fan OFF
Outdoor fan ON
High pressure protection chart
Example
Indoor coil thermistor
RT12 temperature
(MUH-GA50VB) 52˚C
(MUH-GA60VB) 58˚C
(MUH-GA50VB) 48˚C
(MUH-GA60VB) 55˚C
Outdoor fan motor
NOTE : During high pressure protection and for 4 minutes and 15 seconds after high pressure protection, defrosting of
outdoor heat exchanger is not detected by the defrost thermistor RT61.
Released
Cold Air Prevention
<Indoor fan speed>
When the outside temperature goes to 18°C or more.
Until the outside temperature goes to 18°C.
: 52°C
: 48°C
: 58°C
: 55°C
High pressure protection
(MUH-GA50VB)
(MUH-GA60VB)
ON
Fan speed
Set speed
Very Low or stop
18: 22:
Ambient temperature
thermistor RT63 temperature
Released
48:
55:
ON
OFF
30
Outdoor fan speed
13: 18:
Outdoor fan
OFF
ON
52:
58:
Outdoor fan motor
turn OFF
Outdoor fan motor
turn ON
OFF
High
Low