Electrical Control; Expansion Valve; Economizer Valve - Maersk Container Industry Star Cool SCI-20 Operating And Service Manual

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6.4 Electrical control

The following graphical illustration shows the accepted volt/Hz range and the set off values for the
alarms AL 415, AL 418, AL 424, and AL 425.
Supply frequency [Hz]
70
60
50
42,5
40

6.5 Expansion valve

This function ensures optimum evaporator superheat (SH) and calculates the percentage of opening
(SHVod) and controls the valve. This function is active during compressor operation. The valve is
closed during compressor turn off. The expansion valve function includes the following three sub-
functions:
1. MSS (Minimum Stable Superheat search)
This function searches for minimum stable superheat within the ranges SHmin and SHmax.
SHact: = Tsuc - T0 (Psuc)
2. Superheating
Function output is the expansion valve opening rate (Vexp). At start-up the opening rate is 0%.
The electronic expansion valve is an on/off valve controlled on the basis of opening rate with a
constant cycle time.
3. MOP (Maximum Operating Pressure)
The MOP function prevents the suction pressure from getting too high.
Defective sensor(s)
Psuc
Tsuc

6.6 Economizer valve

This function ensures optimum sub cooling of liquid to the evaporator and cooling of the FC. In
addition, the cooling capacity is increased and compressed gas temperature is reduced. Function
output is the economizer valve opening rate (Veco).
The economizer control has two modes:
1. Superheat control
Valve opening rate control is based on calculations.
2. FC cooling
This function is active during compressor operation.
Alarm 425 Unit stop
Alarm 418
(Under voltage)
Unit stop
Alarm 424 Log alarm
300 377
Substitution sensor/Action
Emergency injection
Emergency injection
(Power frequency)
Fans low speed
Fans low speed
(Power frequency)
394
Alarm 415
(Over voltage)
Unit stop
Supply
voltage [Vac]
535 560
Alarm
206, Psuc unrealistic
207, Psuc invalid
126, Tsuc invalid