Another vote for plain r12.

How much are replacement AC components for a RR?
Would you gamble that much $$$ to save $70(perhaps less) on refrigerant?
How much would a proper conversion cost compared to $70 worth of refrigerant?

Now the r12a would be the worst of all possible choices for so many reasons, but I will not start another 'alternative refrigerant bashing' thread here.

r12 prices have dropped to point where a conversion is not really economically viable unless the original system needs extensive repairs. Just don't tell the EPA!

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1986 300E 5-Speed 240k mi.