Service Fee-Platinum Customer found unit to be low on our 410 a unit is approximately 14 years of age furnace is 25+. Do you highly recommend replacing system due to efficiency versus cost?. then explain to customer that prices are inflating end of June. Customer said she will talk it over and possibly call in for a replacement. Add approximately 4 1/2 pounds of our 410a. Vapor saturation right at 38 system utilizes piston. Therefore superheat was targeted at 17. Given wet bulb and drive bulb temperature.