Hitachi SAMURAI Series Service Manual page 55

2. Control Functions
Control of the cooling cycle
2 Protection controls
The basic control follows the contents of section 1, but the following functions are also implemented for the protection
of the product.
a. Low pressure over-increase prevention control
In case of continued operation conditions of low pressure higher than 0.5 MPa, the valve is forced to close and
momentarily set somewhat close in comparison with the opening under normal control.
b. Discharge gas superheat decrease prevention control
During normal operation (during suction gas superheat control), in case of continued operation conditions of
discharge gas superheat temperature lower than 5ºC, the valve is forced to close and momentarily set somewhat
close in comparison with the opening under normal operation.
c. Discharge gas temperature overheat prevention control
In case of continued operation conditions of discharge gas temperature higher than 80ºC, overheating of discharge
gas temperature is prevented by controlling the opening so as to make discharge gas temperature become 75ºC.
d. Evaporated gas temperature decrease prevention control
In case of continued operation conditions of evaporated gas temperature (refrigerant inlet temperature of the water
cooler) lower than -4ºC, the valve is forced to open and momentarily set somewhat open in comparison with the
opening under normal control.
e. Forced control
In case of continued conditions of suction gas superheat higher than 8ºC, with a cold water output setting temperature
higher than 25ºC, the valve is forced to open and momentarily set somewhat open in comparison with the opening
under normal control.
f. 0 (zero) point adjustment control
As a correction of the deviation between the "number of control pulses" and "number of actual pulses" of the
expansion valve opening, generated due to continuous operation over a long period of time, a 0 (zero) point
adjustment is performed "the first time that all compressors are stopped when more than 24 hours have passed
since the last 0 (zero) point adjustment". In case that all compressors are not stopped at once for more than 200
hours (for more than 18 hours in air-cooled heat units), then the compressors are forced to stop status (Forced
thermo OFF), 0 (zero) point adjustment is performed, and they are restarted after a 3-minute guard. It is possible to
cancel this forced 0 (zero) point adjustment from "Service", but it is highly encouraged to leave it "Enabled". If setting
it to "Disabled", protection controls may be activated frequently in case of drastic variations of load.
N O T E
When replacing the expansion valve, please refer to

Image diagram of basic control
Compressor
operation
start
Power ON
Standby at 0 pulses
Zero point adjustment performed upon power ON
47
SMGB0082 rev.1 - 07/2015
£ Starting control II
¢ Starting control I
.
"3.5.1 Compressor removal"
Thermo OFF or stop
§ Starting control II
Superheat control
Time
Standby at 0 pulses
2