Msz, Msy Microprocessor Control; Cool Operation - Mitsubishi Electric MS-A WA Service Technical Manual

2

MSZ, MSY MICROPROCESSOR CONTROL

2-1. COOL ( ) OPERATION
1. Thermostat control
Thermostat turns ON or OFF by the difference between room temperature and set temperature.
Thermostat
2. Indoor fan speed control
Indoor fan operates continuously at the set speed by FAN SPEED CONTROL button regardless of the thermostat's OFF-
ON.
In AUTO the fan speed is as follows.
Fan speed
3. Coil frost prevention
The compressor operational frequency is controlled to prevent the temperature of indoor heat exchanger from falling exces-
sively.
The compressor is turned OFF for 5 minutes when the temperature of indoor coil thermistor continues 37°F (3°C) or less for
5 minutes or more.
The indoor fan maintains the actual speed of the moment.
4. Low outside temperature operation
If the outside temperature falls to 64°F (18°C) or less during operation in COOL mode, the unit will switch to the low outside
temperature operation mode.
<Operation>
(1) Outdoor fan control
The outdoor fan rotational speed slows down to maintain sufficient cooling capacity.
NOTE: Even when the unit is in the "thermostat-off" status under the low outside temperature operation mode, the out-
door fan rotation does not stop.
(2) Dew drop prevention
When the ambient temperature thermistor reads 14°F (-10°C) or less (the set temperature is different depending on the
models), as coil frost or dew drop from indoor unit may occur, the compressor turns OFF with the outdoor fan OFF for
prevention of them.
(3) Outdoor temperature detecting control
To detect the exact outdoor temperature in this mode, the compressor turns OFF but the outdoor fan stays ON for 3
minutes once 1 hour. If the outdoor temperature rises over about 64°F (18°C), the unit goes back to the normal COOL
mode. If the outside temperature stays below about 64°F (18°C), the unit continues to run in the low outside tempera-
ture operation mode.
Other protections work as well as in the normal COOL mode.
ON
OFF
Room temperature minus
set temperature (Initial)
High 3.15°F(1.75°C) or more
Med. between 1.8 and 3.15°F
Low
less than 1.8°F(1°C)
Room temperature minus
set temperature (Initial)
-1.8°F(-1°C) or more
less than -1.8°F(-1°C)
7
Room temperature minus
set temperature (During operation)
-1.8°F -1.35°F
(-1°C) (-0.75°C)
Room temperature minus
set temperature (During operation)
5.4°F
(3°C)
3.15°F
1.8°F
(1.75°C)
(1°C)