Hitachi RAS-2-HVNP Service Manual page 195

7. Test run
Additional information for "Check list on compressor"
Check item
The liquid refrigerant return volume to the compressor is controlled by the discharge gas temperature Td when
compressor is operating. If Td thermistor is disconnected, the liquid refrigerant return volume will become small
1 & 2
by detecting the temperature even if the actual discharge gas temperature is high. Therefore, this abnormal
overheating by detecting the temperature operation will result in insulation failure of the motor winding.
Overcurrent control (operating frequency control) is performed by detecting current by the PCB2. In this case,
3 & 4
winding insulation failure will occur, since control is not available in spite of actually high current.
The current sensor checks phase and adjusts output electrical wave in addition to the above mentioned items. If
5 & 6 fault occurs, the output electrical wave becomes unstable giving stress to the motor winding, resulting in winding
insulation failure.
During a cooling operation, SH is controlled by MV of each indoor units. During a heating operation, Td is
controlled by MV1. If expansion valves are incorrectly connected, correct control is not available, resulting in
7 & 8
compressor seizure depending on liquid refrigerant returning conditions or motor winding insulation failure de-
pending on overheating conditions.
If the refrigeration cycle and electrical system are incorrectly connected, abnormally low suction pressure ope-
9 ration is maintained or abnormally high discharge pressure operation is maintained, resulting in giving stress to
the compressor, since their correct control is not available.
If the expansion valve and electrical system are incorrectly connected, abnormally low suction pressure opera-
10 tion is maintained or abnormally high discharge pressure operation is maintained, resulting in giving stress to
the compressor, since their correct control is not available.
11 The compressor may be locked due to the liquid return operation during the cooling operation .
In the case that the contacting resistance becomes big, voltage imbalance among each phase will cause abnor-
12
mal overcurrent.
13 In this case, overcurrent will occur, efficiency will decrease or the motor winding will be excessively heated.
14 In the case, it will result in motor burning or compressor failure
181
SMGB0079 rev.0 - 01/2013
Additional information (mechanism of compressor failure)
7