2-24
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 tempe1.0˚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 to suppress high pressure and starting current.
™
Temperature control of refrigerant oil
When ambient temperature is low, the temperature of 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.
In order to control the oil temperature of refrigerating unit or in
the event the high pressure is low, operate the compressor with
the condenser fan stopped. If the high pressure reaches 1500
kPa or more, the fan will restart to operate.
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 stop time of 10
sec. is provided to switch the high speed to low speed and vice versa.
Chilled 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.
+ 2 ˚C
+ 1 ˚C
– 1 ˚C
ON
OFF
Set point
temperature
Compressor
1 minutes
2 minutes compressor forced operation
Time
Return air temperature
ON
OFF
1500kPa
1300kPa
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