I would stick with R12. I had my system changed to R134 and I have never been happy. I hope to have it converted back this week. This is on my 89 300SEL. The A/C is ice cold going down the highway but in stop and go trafic you might as well be riding with the windows down. When I did my change over, I had the entire system replaced .

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Mike

90 300D 511k
95 C280 133k
14 BMW 528i