Hello folks 20 yr Virginia HVAC tech here, 407 and R22 are pretty much the same animal, some will say interchangeable, but are forgiving oil wise, I’ve worked on many blown out systems that sat open all winter and were successfully repaired in spring
I’ve got 5 Drash units haven’t seen any with drilled holes Butner NC yet.
if you get unknown AC units with no refrigerant first thing you wanna do is power ECU unit up and bump the contactor see if compressor is good, if it runs and doesn’t make horrible noises it’s prolly fine, Even with no refrigerant low side will pull a vacuum if she’s pumping, Remember scroll compressors are phase dependent!!
next thing you wanna do is pressure test with nitrogen and see if it’s gonna hold pressure, let it sit for 24hrs +. No sense in dumping refrigerant into a slow leaker, Weld / braze any leaks and retest.
if you have gotten this far, change the filter dryer and pull a good deep vacuum on it, the longer the better, the hotter the ambient air the better,
check rated charge, put about 1/2 charge into high side, crank it up make sure everything is happy, slowly put remaining charge in low side while compressor is running
I’ve repaired several 22 systems with actual water in the system, deep vacuum and way oversized filter dryer, (changed after a month) it’s still running yrs later