Hitachi RCUE40AG2 Service Manual page 81

Control system
In this series, electronic expansion valve is used. Electronic expansion valve is consisted in the body (fi gure), Coil,
and PCB for expansion valve running (PCB
1. The range of opening of expansion valve
The opening of expansion valve is managed by pulse number. The range is 116~656 pulse. During stop, it is
stand-by with 10 pulse.
2. PCB for expansion valve running
PCB (VD PCB) is used. The pulse number of the opening of expansion valve is indicated in the segment on
G
VD PCB.
3. Zero point adjustment
Zero point is adjusted by initialization at power ON. The order of opening of expansion valve is closed fully
(less than 0 pulse) and both control pulse number recognized in micro computer and real pulse number are
adjusted to zero. During this adjustment, "Cn-Eo" is indicated in the segment. (n= Unit No.)
Zero point adjustment is also performed " at the fi rst compressor stop after 24 hours since the last zero point
adjustment"., to modify the error between control pulse number and real pulse number. If compressore has
not stopped for over 200 hours, compressor is to be stopped forcedly (forced Thermo OFF) and zero point
is adjusted. Then, unit is re-started after 3 minutes guards. It is possible to cancel this forced zero point
adjustment by Dip Switch selection on expansión valve PCB.
4. During normal operation
Temperature of compressor suction gas superheat is calculated from the temperature detected by Thermistor
of compressor suction refrigerant gas and the pressure detected by the sensor for suction pressure, and the
opening is determined by calculation value to reach target superheat. (Control cycle: 28 seconds)
5. Prevention control for discharge refrigerant gas overheat
When discharge gas refrigerant temperature is over 100°C, expansion valve is opened forcedly and excess
increase of discharge gas refrigerant temperature is prevented. (Td control).
pag. 79
SMGB0003 rev.0-01/2007
(VD PCB)).
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