When using old linesets, linesets are either blown with nitrogen or flushed with a solvent when switching from R22 to 410a. It is often recommended that linesets should always be replaced. I noticed that commercial refrigeration guys just dump the mineral oil out and replace it with POE when doing refrigerant changes. I think copeland even says 5 percent mineral oil is fine when doing a conversion. Why is there so much concern for mineral oil/ POE mixing in a residential system and not commercial refrigeration?