Evaluating And Adjusting Refrigerant Charge; Refrigerant Overcharge And Undercharge; Checking The Refrigerant Charge During Operation; Maximum Refrigerant Charge - Mitsubishi Electric HP120TNU-A Service Handbook

[6-3 Evaluating and Adjusting Refrigerant Charge ]

6-3

Evaluating and Adjusting Refrigerant Charge

6-3-1

Refrigerant Overcharge and undercharge

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.
The system comes to an abnormal stop, displaying 1500 (overcharged refrigerant) on
the controller.
The operating frequency does not reach the set frequency, and there is a problem with
performance.
The system comes to an abnormal stop, displaying 1102 (abnormal discharge temper-
ature) on the controller.
6-3-2

Checking the Refrigerant Charge during Operation

Operate all indoor units in either cooling-only or heating-only mode, and check such items as discharge temperature, subcool-
ing, low pressure, suction temperature, and shell bottom temperature to estimate the amount of refrigerant in the system.
Discharge temperature is high. (Normal discharge temperature is below 95°C [203°F].)
Low pressure is unusually low.
Suction superheat is large. (Normal suction superheat is less than 20°C [36°F].)
Compressor shell bottom temperature is high. (The difference between the compressor shell
bottom temperature and low pressure saturation temperature (Te) is greater than 60°C [108°F].)
Discharge superheat is small. (Normal discharge superheat is greater than 10°C [18°F].)
Compressor shell bottom temperature is low. (The difference between the compressor shell bot-
tom temperature and low pressure saturation temperature (Te) is less than 5°C [9°F].)
6-3-3

Maximum refrigerant charge

There is a limit to the amount of refrigerant that can be charged into a unit. Observe the maximum refrigerant charge in the
table below.
HP72-240Y(T)(S)NU-A
Total index of the outdoor units
Factory charge (kg) (oz)
Maximum additional refrigerant
charge on site (kg) (oz)
Maximum refrigerant charge (kg) (oz)
HWE18220_GB
Symptoms
P72 P96 P120
5.2 8.0 8.0
(184) (283) (283)
28.3 33.5 39.5
(999) (1182) (1394)
33.5 41.5 47.5
(1182) (1464) (1676)
Overcharged refrigerant
Insufficient refrigerant amount
Conclusion
Slightly under-
charged refrigerant
Slightly overcharged
refrigerant
P144 P192 P240
10.8 16.0 16.0
(381) (565) (565)
38.5 58 74
(1359) (2046) (2611)
49.3 74 90
(1739) (2611) (3175)
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