Hitachi RAS-2-HVNP Service Manual page 302

8. Troubleshooting
Additional Information for "CHECK LIST ON COMPRESSOR"
Check item
1 & 2 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 by detecting the temperature even if the actual discharge gas temperature is high. There-
fore, this abnormal overheating by detecting the temperature operation will result in insulation failure of
the motor winding.
3 & 4 Overcurrent control (operating frequency control) is performed by detecting current by the PCB2.
In this case, winding insulation failure will occur, since control is not available in spite of actually high
current.
5 & 6 The current sensor checks phase and adjusts output electrical wave in addition to the above mentioned
items. If fault occurs, the output electrical wave becomes unstable giving stress to the motor winding,
resulting in winding insulation failure.
7 &8 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 compressor
seizure depending on liquid refrigerant returning conditions or motor winding insulation failure depend-
ing on overheating conditions.
9 If the refrigeration cycle and electrical system are incorrectly connected, abnormally low suction pres-
sure operation is maintained or abnormally high discharge pressure operation is maintained, resulting in
giving stress to the compressor, since their correct control is not available.
10 ditto
11 The compressor may be locked due to the liquid return operation during the cooling operation.
12 In the case that the contacting resistance becomes big, voltage imbalance among each phase will
cause abnormal 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 seizure.
288
SMGB0079 rev.0 - 01/2013
Additional information (mechanism of the compressor failure)