The charge is the total mass of refrigerant circulating in the system (kg), and every system has its own correct value: it depends on evaporator and condenser volume, pipe length, receiver size and refrigerant. It may be 0.5–2 kg in a small monoblock, 5–20 kg in a medium cold room system and hundreds of kilograms in central systems.
Charging is done into the evacuated system as liquid (mandatory for zeotropic refrigerants, preferred for the others) through the liquid line, or in a controlled way through the suction while running. The correct quantity is recognised as follows: sight glass clear, superheat 5–10 K, subcooling 3–8 K, pressures consistent with the ambient temperature. Charging by the sight glass or the pressure alone is the most frequent cause of overcharging.
Undercharge: low suction pressure, high superheat, low capacity, iced expansion valve, hot compressor. Overcharge: high condensing pressure, high subcooling, high consumption, risk of liquid floodback. Every charge and top-up must be recorded under the F-gas regulation and the refrigerant must be charged by a certified technician; GWP × charge quantity determines the leak check frequency. You can check the correct pressure–temperature values in our refrigerant chart.