I had the same issue and converted my 190E to R-134A four years ago. I changed the drier at that time and then evacuated the system for about two hours. Recharged the system normally with R-134A and two cans of oil charge for R-134A. It's been fine since. There does seem to be some small loss of efficiency but the A/C seems to work well. At $4 / pound it's a lot more cost effective and it's readily available.