Everything Iv'e learned, being in the Supermarket Refrigeration biz for 20 yrs. seems to be out the window. ( well, not everything) I have been involved in a gas conversion program with a major Supermarket chain in the midwest for the past two months or so, and quite a few more to do. Converting R-22 to R-507 (Rack systems). I have done many conversions in the 90's going from R-502 to R-507 and 404-a. The mystery is this time around, realizing (by theory) we need to change txv's and change out or drill out distribitor orfices at the evaps.(expecially walk-ins) what we found, by accident(overlooked fixtures we missed replacing valves in) there was no differance in superheat with valves change to the correct application verses leaving the R-22 valves in. (these were the same mod.# cases) The other confusing thing was, instead of changing the whole valve body on the sub-cooler valves, we oppted to change just the power heads. thinking we would have to open the valve a bit to achieve proper superheat.To my surprise, we were flooding back soooo much that the compressors turn white in a very short time. could not adjust the valves to back off the liquid slugging.We put the R-22 powerheads back on and now it's fine. Any words of wizdom would be greatly appreciated.