Sorry folks, but the patent on Freon ran out long ago, sometime
before 1974. At NASA-Langley we had a wind tunnel that flowed
Freon rather than air and when the patent ran out, the cost to
supply the wind tunnel dropped in half because of competition.
Patents are only for 17 years (generally, some specific situations
can modify it slightly) and Freon has been around a long time.

Frank Herzig
'85 Vanagon, with AC but took the compressor belt off long ago.