If you are adding refrigerant in an effort to get the suction pressure up or to reduce the evaporator superheat and the only change you see is the head pressure going up while the liquid line gets cooler, then you have a restricted or undersized orifice. The superheat slide chart appears to make everything simple. In most cases it does. But in those other cases you must understand the logic of both the chart and of the manufacturer who designed the chart. The chart is to guide you in securing a satisfactory result for your customer and to avoid nuisance callbacks that are harmful to the bottom line and your reputation.
Regulations seem to be ever changing.
Many companies have financial interests in promoting scare tactics used in selling refrigerant usage tracking systems and software. Our company works on no systems with more than 50 lbs. of refrigerant charge.