I would suggest that you do whatever research is necessary to find the specified R12 volume and work from that number. That said, in the case of a 134a conversion, it might not be that big of a deal anyway. Charging an R12 system with 134a is a mixture of rolling dice and black magic.

Start with a very low volume and work up SLOWLY.

Is it impossible for you to obtain and use R12? What have you done to prepare for the 134a conversion?

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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