Piecing together an A/C system

The main efficiency comes from having a larger condenser and parallel-flow is 30% more efficient for the same size. Duracool claims their "Oil Chill" is more efficient since stays in the compressor better. I think that is Hella PAO 68 which is the best oil - doesn't absorb moisture to form acids like PAG and compatible with all refrigerants. You must have a low-pressure port to be able to fill. A high-pressure port is nice for ideal monitoring, though the low port is good enough to tell if a proper refrigerant charge (should be 30-50 psig on 70 F day after sitting long). I put a small pressure relief valve in the outlet of one of my Sandens, which will vent if >300 psig. That may keep the compressor from stalling on a very hot day (108 F) to burn-up the clutch, which happened in two of my cars (OEM compressor), but you won't see such days unless you drive to Anatolia (49 C record in 2021). Illegal to vent per U.S. EPA, but w/ HC no worries.