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Common control
A : Compressor ON/OFF control
When the control temperature reaches the set temperature or lower, the compressor is stopped.
When the control temperature rises and becomes higher than the [set point temperature +1.0˚C], the
compressor runs again.
When the compressor starts running it is forcibly run for 2 minutes. (2 minutes compressor forced
operation) in order to prevent the compressor from deterioration due to shortage of lubricant.
B : Starting control
™Control when protective device activated
When the high pressure rapidly rises on starting or when the starting current is overcurrent, the
compressor automatically stops and starts to suppress high pressure and starting current.
™Temperature control of refrigerant oil
When ambient temperature is low, the temperature refrigerant oil for compressor is also low and
the viscosity of the oil may be high.
On starting the unit, by-pass discharge gas to suction side of the compressor by opening the
solenoid valve (BSV) to raise the oil temperature rapidly ensuring a stable feed of oil.
The temperature control for refrigerant oil should be executed not with power ON/OFF in normal
operation but with power ON under low ambient temperature.
An oil temperature raising control can be executed when all of the following conditions are met.
• The time turning power supply ON
• Ambient temperature ≦ 10˚C
• (Discharge gas temperature – ambient temperature) ≦ 4˚C
C : Evaporator fan speed control
The speed of the evaporator fan is switched in accordance with operation modes. A delay time of 10
sec. is provided to switch the high speed to low speed and vice versa.
Chilled mode : High speed
Partial frozen mode : High speed
Frozen mode : Low speed
D : Superheat control
The evaporator superheat is adjusted to be optimum by controlling the opening of the electronic
expansion valve, based on the evaporator inlet and outlet refrigerant temperature, and the
compressor suction gas temperature.
E : High-pressure control
• By electronic expansion valve
When the ambient temperature is high during the air-cooled operation, the condensing pressure
(high pressure) will increase, and the high pressure switch may be activated.
In order to prevent this situation, the high pressure is controlled to be 2350kPa or lower by
adjusting the opening of the electronic expansion valve.
• By condenser fan
When the ambient temperature is low during the air-cooled operation, the condenser pressure
(high pressure) will decrease. Accordingly, the low pressure will decrease.
In order to prevent this situation, when the high pressure becomes set point or lower, the
condenser fan stops to prevent the high pressure from excess dropping.
When the high pressure becomes set point or higher afterwards the operation will be restarted.
This control varies upon dehumidification setting.
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