Adjusting The Refrigerant Amount - Mitsubishi Electric City Multi PQHY-P72 Service Handbook

[ 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 system.
Then, adjust the refrigerant amount by running the unit in the refrigerant amount adjust mode.
1 The system comes to an abnormal stop, displaying 1500 (overcharged refrigerant) on
the controller.
2 The operating frequency does not reach the set frequency, and there is a problem with
performance.
3 The system comes to an abnormal stop, displaying 1102 (abnormal discharge temper-
ature) on the controller.
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 Discharge temperature is high. (Normal discharge temperature is below 95°C [203°F].)
2 Low pressure is unusually low.
3 Suction superheat is large. (Normal suction superheat is less than 20K [36°F].)
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 [108°F]. )
5 Discharge superheat is small. (Normal discharge superheat is greater than 10K[18°F].)
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 [9°F].)
Symptoms
- 160 -
Overcharged refrigerant
Insufficient refrigerant amount
Conclusion
Slightly under-
charged refrigerant
Slightly overcharged
refrigerant