Mitsubishi Electric PU(H)Y-P250YGM-A, Service Handbook

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[
VIII
Test Run Mode ]
[4] Adjusting the Refrigerant Amount
1. Symptoms
Overcharging or undercharging of refrigerant can cause the following symptoms :
Before attempting to adjust the amount of refrigerant in the system, thoroughly check the operating conditions of the sys-
tem. Then, adjust the refrigerant amount by running the unit in the refrigerant amount adjust mode.
2. Amount of refrigerant
(1) To be checked during operation
Operate all indoor units in either cooling-only or heating-only mode, and check such items as discharge temperature, sub-
cooling, low pressure, suction temperature, and shell bottom temperature to estimate the amount of refrigerant in the sys-
tem.
1 The system comes to an abnormal stop, displaying 1500 (overcharged refrigerant) on
the controller.
Overcharged refrigerant
2 The operating frequency does not reach the set frequency, and there is a problem with
performance.
Insufficient refrigerant amount
3 The system comes to an abnormal stop, displaying 1102 (abnormal discharge temper-
ature) on the controller.
Symptoms Conclusion
1 Discharge temperature is high. (Normal discharge temperature is below 95°C.) Slightly under-
charged refrigerant
2 Low pressure is unusually low.
3 Suction superheat is large. (Normal suction superheat is less than 20K.)
4 Compressor shell bottom temperature is high. (The difference between the compressor shell
bottom temperature and low pressure saturation temperature (Te) is greater than 60K.)
5 Discharge superheat is small. (Normal discharge superheat is greater than 10K.) Slightly overcharged
refrigerant
6 Compressor shell bottom temperature is low. (The difference between the compressor shell bot-
tom temperature and low pressure saturation temperature (Te) is less than 5K.)