Well, for a counter point to the evil blend theory:
Taken this morning on the way to work.
Freeze12 works very nicely for me. Much better than R134a and not much different than R12. The blend thing hasn't been an issue even though I've added 1/3 to 1/2 a can for the last 2-3 summers. Have had this system and compressor working for about 5 summers now.
Most folks knocking Freeze12 have never tried it. Nothing like actual experience with a particular product to kind of validate the opinion, eh?
I'm just sayin'........
btw, I will look for my pressure data tomorrow and report back if I can find it. You use the chart on the Freeze12 site and add 40 degrees to your ambient temp and go with those pressures. Seems like Al's high side pressure is about right with temps in the 90's, but I don't remember the low side being as high as 40.