Charge levels within 20 percent of manufacturer specs protect HVAC efficiency during refrigerant transitions

https://blogfreely.net/lithilszxt/a-2000-square-foot-home-needs-3-5-to-4-tons-for-ideal-operating-costs

The 20 rule in HVAC refers to the refrigerant charge level that must stay within 20 percent of the manufacturer's specification to maintain efficiency and avoid compressor damage