An article in a recent Cars & Parts said the same thing as Joe. Apparently R-134 isn't environmentally friendly enough. There's some new stuff in the works, R-433 or thereabouts, that will require even more pressure and will be less efficient. They also said that some sort of variable valve is recommended in a changeover from R-12 to R-134. --Roger van Hoy, '55DeSoto, '42DeSoto, '66Plymouth, '73Duster, '81 Imperial, Washougal, WA