Hitachi FS3 Series, Service Manual, Page: 185 / 240

3
MAIN PARTS
13
3.4. PRESSURE SENSOR
n
High Pressure Control
The high pressure during heating operation is detected by a
high pressure sensor, and compressor frequencies are
controlled by the proportional controlling method with
operating capacity of indoor units so that the high pressure is
controlled in an appropriate range. The output of the high
pressure sensor during heating operation performs protective
control; gas by-pass control.
High Pressure Sensor
Output Volta
g
e (DCV)
Pressure MPa (kgf/cm²G)
Output Characteristics of High Pressure Sensor
n
Low Pressure Control
The suction pressure during cooling operation is detected by
a low pressure sensor, and compressor frequencies are
controlled by the proportional controlling method with
operating capacity of indoor units so that the suction pressure
is controlled in an appropriate range. If the suction pressure
reaches excessively low, the cooling can be insufficient and
parts composing the refrigeration cycle can be damaged. For
this reason, if the output of the low pressure sensor indicates
vacuum and the valve is maintained 12 minutes or longer, the
compressor is stopped for the purpose of protection.
Low Pressure Sensor
Output Volta
g
e (DCV)
Pressure MPa (kgf/cm²G)
Output Characteristicsof Low Pressure Sensor
Heating Operation
Proportional Control of
Compressor Frequency
with Operating Capacity
of Indoor Units
Protective Control Gas
Bypass Valve Check
Cooling Operation
Proportional Control of
Compressor Frequency
with Operating Capacity
of Indoor Units
Vacuum Preventive
Control
HIgh
Pressure
Control
Low
Pressure
Control