Just Googled up "es-12 pressure temperature chart" and got their home page: http://www.befreetech.com/envirosafe.htm It's difficult to read, partly because they screwed up their HTML.

Another option might be to search for other users of hydrocarbon refrigerants and see what is their experience. There used to be an alternative refrigerants discussion at www.aircondition.com, but they appear to have gone PC. There are some old discussions laying about: http://www.aircondition.com/wwwboard/alternative/current/7348.html and http://www.aircondition.com/wwwboard/alternative/index.htm

Hmmm. The 2nd link says hyrdocarbon blends don't cool well at idle. Oh well, give it a read and let us know what you learn.

- JimY