Whether the ac was on tractor when bought new from dealer or added later,non are STANDARD. Hose length ,different metering devices,size and a host of other details require charging by super heat or other means. Unless showed how by an experienced tec, ac charging is best left to a pro. Unintentionally introducing air, contaminates and moisture into system ultimately damages system costing more to repair than had charging been done right to begin with.
Sorry I rained on the parade but here's something everyone that wants to diy despite what I say can use. While installing new ac or during a repair that requires opening system,install a sight glass in high side line.