❓ Why is deep vacuum evacuation (<500 microns) required before gas charging?

Modern refrigerants like R-32 and R-410A use synthetic Polyolester (POE) oil which is extremely hygroscopic (absorbs moisture from air). Moisture mixes with refrigerant to create hydrofluoric acid that eats compressor motor insulation. Pulling vacuum below 500 microns boils away all moisture and non-condensables.