What year??

If it holds a charge for a couple of months, you have a leak. Where a sniffer, or dye will let you know.

The R12 to R134 conversion without flushing the oil out is not good. The R12 oil is not compatable with the R134 oil so neither will stay in suspension and do there job. eventually the compressor will fail due to lack of proper lubrication.

Do a search on R12 to R134 conversion. I did mine (correctly, I am licensed) and went back to R12 due to the lack of cooling with R134. Plenty of info and debate on the R12 to R134 conversion in the W123 body ( if your car is a W123).

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car