Every refrigeration circuit is designed around a specific mass of refrigerant. Too little and the evaporator is starved: the cabinet cools slowly, the compressor runs long and gets hot because the returning gas is not cooling it properly. Too much and liquid can back up in the condenser or flood back to the compressor, raising pressures and power draw and risking damage.
Small commercial cabinets with capillary tubes carry a small, critical charge, often a few hundred grams or less. On hydrocarbon units the charge is deliberately kept low for safety. The correct method is to recover any remaining refrigerant, repair the leak, replace the filter drier, evacuate with a vacuum pump and then weigh in the rated charge on a scale. Topping up by watching a gauge needle is guesswork.
A sealed system does not consume refrigerant. If a unit needs gas, it has a leak, and the leak must be found and fixed. Common leak points in Indian kitchens are corroded joints near drains, rubbed tubing behind the cabinet and pin-holes in evaporators exposed to acidic food vapours.