The system is under pressure. It will freeze your hands by simply disconnecting the drier!! So, remove freon with a recovery machine, then remove/replace drier. Then vacuum system down, then add 134. If 134 is low, it has a leak somewhere. When you add the 134 add leak detection dye to the system and check for a leak in 2 weeks.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.