Expansion Valve Control - Hitachi SAMURAI Series Service Manual

2 Control Functions
Control of the cooling cycle

2.2.2 Expansion Valve Control

The expansion valve used in this product is an electronic expansion valve. The electronic expansion valve is composed
by the main unit and a coil. The control functions of the electronic expansion valve are as shown below.
1 Basic control
 0 (Zero) point adjustment
Compressor startup
¢ Starting control I
£ Starting control II
 Normal control
Compressor stop
 Stop control
10
8
5
3
20 25 30
Cold water outlet setting temperature (ºC)
37 SMGB0120 rev.0 - 11/2017
Power ON
No
Yes
No
Yes
 0 (zero) point adjustment
0 (zero) point adjustment is conducted as an initialization
(detection of base point) upon power ON. This control is
performed to make the control pulses recognized by the
microprocessor and the actual pulse number to match
at 0, by outputting a full closure order (under 0 pulse) for
the opening of the expansion valve. During execution,
the operation information of the LCD screen displays
"Adjusting 0 (zero) point of the expansion valve", while
the segment display becomes "Cn-E0" (n stands for unit
number).
¢ Startup control I
The opening is predetermined for 1 minute after
compressor startup.
£ Startup control II
The opening is controlled within a predetermined amount
of variation until the discharge gas superheat (TdSH),
which is calculated from the high pressure detected by
the high pressure sensor (Pd) and the discharge gas
temperature detected by the thermistor (Td) can be kept
above 10ºC.
 Normal control
The opening is controlled to achieve the target value of
suction gas superheat (TsSH), which is calculated from
the low pressure detected by the low pressure sensor
(Ps) and the suction gas temperature detected by the
thermistor (Ts).
Also, in the case of cooling operation, the target value of
TsSH is calculated from the setting value of cold water
outlet temperature, as shown in the figure below.
 Stop control
After compressor stop and setting to full closure, standby
at 0 pulses.
?
N O T E
The opening range used during the operation of the expansion valve
lies between 120 and 5960 pulses.
2