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Operation Characteristics And Refrigerant Charge; Evaluating And Adjusting Refrigerant Charge; Refrigerant Overcharge And Undercharge; Checking The Refrigerant Charge During Operation - Mitsubishi Electric PURY-HP72 Service Handbook

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[6-8 Operation Characteristics and Refrigerant Charge ]

6-8

Operation Characteristics and Refrigerant Charge

It is important to have a clear understanding of the characteristics of refrigerant and the operating characteristics of air conditioners
before attempting to adjust the refrigerant amount in a given system.
The following table shows items of particular importance.
1) During cooling operation, the amount of refrigerant in the accumulator is the smallest when all indoor units are in operation.
2) During heating operation, the amount of refrigerant in the accumulator is the largest when all indoor units are in operation.
3) General tendency of discharge temperature
Discharge temperature tends to rise when the system is short on refrigerant.
Changing the amount of refrigerant in the system while there is refrigerant in the accumulator has little effect on the discharge
temperature.
The higher the pressure, the more likely it is for the discharge temperature to rise.
The lower the pressure, the more likely it is for the discharge temperature to rise.
4) When the amount of refrigerant in the system is adequate, the compressor shell temperature is 10 to 60°C [18 to 108°F] higher
than the low pressure saturation temperature (Te).
-> If the temperature difference between the compressor shell temperature and low pressure saturation temperature (Te) is
smaller than 5°C [9°F], an overcharging of refrigerant is suspected.
6-9

Evaluating and Adjusting Refrigerant Charge

6-9-1

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.
6-9-2

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].)
HWE13080
Symptoms
- 161 -
Overcharged refrigerant
Insufficient refrigerant amount
Conclusion
Slightly under-
charged refrigerant
Slightly overcharged
refrigerant
GB

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