I note they talk about evacuating the refrigerant system for 30 - 60 minutes. The typical GT40 system with condenser in front of the radiator has a lot of refrigerant piping and/or tubing, so needs longer than this. After leak testing, when you are satisfied with the integrity of your piping system and all its joints, pump down to a vacuum and maintain this for at least three hours. This low pressure boils off the moisture in the refrigerant piping before (of course) you add the refrigerant. To get completely rid of all the moisture in such an extenaive system from mid-engine compressor to front condenser and cockpit evaporator/fan-coil, you need to maintain the pumped down pressure for several hours. Otherwise the moisture contamination reduces the performance of the refrigerant. Just my 2c worth.