Ack, another A/C thread. If you use the search function you can find a lot of info on this subject. To quickly answer your questions: 1. The only thing that absolutely needs to be replaced is the drier. Any time the system is cracked open you should replace the drier. Many people will replace the expansion valve, and compressor on a R134a conversion b/c the oil used w/ that refrigerant turns into something pretty acidic if there's any moisture in the system. Therefore, a leak typically means that you're asking for trouble down the line.

Have you considered simply fixing the leak and keeping R12 in your system? Your perfomance will be much better as you really can't get optimum R134a permforance in a vehicle not designed to use it originally.

Please note that you will need to evacuate, thoroughly flush your system (especially if you've had compressor failure) and vacuum it down to remove all moisture before adding refrigerant and oil.

Finally, the heat issue is a common one. Your monovalve probably failed. Again, a search will get you all the information (and probably pictures) that you need.

Good luck.

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Tjohn

82 300 SD
77 450 SL (gone)