"Freon" is a possible problem here. I think a 90 is still an R12 car if it hasn't been converted to a newer refrigerant yet. Don't just throw a can of refrigerant in until you know what the car needs.There are differences in the fittings to prevent mixing the two but sometimes people put an adapter fitting on without doing a proper conversion to a newer refrigerant. R134a and R12 are not compatible and some of the "substitutes" for R12 are junk and will cause you trouble. There are many who believe that all of the "substitutes" are junk. I've just been doing without air cond rather than deal with the headache.
Regards, Eric

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89 300E "Benzer1" 15.924 Uncorrected
93 400E "Benzer3" 14.200 U.C.
95 E420 "Benzer4"
92 300E "Benzer5" 16.299 U.C. Future turbo CNG
87 300D "Benzer7"
87 300D "Benzer8"
87 300D "Benzer9"
87 300D/70 AMC Javelin "Sidewinder-Benzer"
87 300TD "Benzer11"
06 E320 CDI "Benzer12"
05 E320 CDI "Benzer12A"
71 AMC Javelin AMX 401 "Sidewinder"
74 AMC Hornet 401 "C.K.10" 13.63 U.C.
74 Bricklin SV1 "Presto" AMC 360 pwrd.