That is one of the  down sides of freeze 12.  Most folks dont concern
themselves with the need for future service and add freeze12.

Another down side is that freeeze12 is a blend of two refrigerants and a
bit of a/c flush. One will leak out faster than the other, and your
concentrations will never be the same as when first added to your system.

Maggie, anyone who can put a subaru engine in a vanagon, and re do the
wiring harness themselves, can fix an a/c problem. YOu can add oil to
thecompressor , and charge is up during the comercials while watching your
evening tv.