Refrigerant is not consumed. If the charge is low it has gone somewhere, and pumping more in without finding the escape wastes your money and vents gas into the atmosphere.
We pressure-test with dry nitrogen, sweep the joints and coil faces with an electronic detector, and introduce dye only when a leak is slow enough to need it. Once the escape route is repaired, the system is evacuated and an accurate charge is weighed in.
You get the before and after readings in writing: suction pressure, superheat, subcooling and the delta-T across the coil.
