What type of refrigerant is used for a dutchman RV air conditioner?

Need to know the year of manufacture. 1995 or newer will be R134A. 1991 or older will be R-12. 1992 - 1994 will most likely be R-12, but may possibly be R-134a.

If your vehicle is pre-95 and you're not the original owner, I'd recommend that you take it to a shop and have them perform a refrigerant purity test. Many R-12 systems were later retrofitted to R-134A, and this cannot be determined by visual inspection, since these systems usually retained the R-12 schrader valves even after conversion to R-134a.