Sorry to be a thread hog just my brain is cooking this one. Split systems are best charged by subcool or superheat IMO. Weighing a charge should be for something that there is not a variable in ,i.e. ice machines and package units or fridges. The line set of a split system is a variable unless you know for a fact EXACTLY how long the lines are. Which makes weighing a charge for a split a tad trickier to do. It can be done ,but only with accurate math.