Refrigerant charge
Also known as: charging, gas charging, charge quantity
Short definitionBoth the total amount of refrigerant in the circuit and the job of filling that amount into the system. If it is short, capacity drops; if too much is put in, pressure rises. The right amount is found by measuring superheat and subcooling.
In a quote the refrigerant is a separate line, written in kilograms. The amount is set by the internal volume of the evaporator and condenser, the size of the receiver, the type of refrigerant and most of all the pipe run; when the outdoor unit is placed far away, the item grows. A small monoblock runs on 0.5–2 kg. A medium room system takes 5–20 kg and a central system hundreds of kilos. Charge multiplied by GWP shows how often leak checks are due; every fill and top-up is recorded.
Charging is done through the liquid line into an evacuated circuit; a zeotropic blend is charged in the liquid phase only. Three signs show the amount is right: there are no bubbles in the sight glass, subcooling is between 3 and 8 K and superheat between 5 and 10 K. A fitter who trusts only the sight glass or the gauge usually overcharges. In an undercharged system suction pressure is low, the compressor is hot and capacity falls short. With overcharge, condensing pressure and electricity consumption go up.