I had a prospective heat pump installer, seasoned guy, been doing this a long time, told me he doesn't purge with nitrogen when installing new line sets. I don't know what his record is like, but the distributor recommended him. (maybe he gives them a lot of business lol). I also seemed to hear him say it's not necessary to "pull a vacuum" either. Aren't these Standard Operating Procedures or maybe experience outweighs ???