I had heard that 409 was not recommended for cars, but forgot the reason. Also, I seem to recall seeing a TP chart as well as a graph that compared it to 12. The graph had the temp horizontally and the pressure vertically. It seems to me that around 30 deg more or less, the 409 pressure was actually lower than that of 12, but as the temp increased, it got higher than 12. but the two lines stayed fairly close throughout the normal temp range found in refrigeration, but at a certain point the
409 line shot damn near straight up. I don't remember what that temp was, but it was well within the range of what you could expect to see on auto a/c. When I worked in refrigeration, we used a lot of 409 in ice machines and it worked great. It is not good for cars, or small cap tube systems. FWIW, I dumped two cans of Freeze 12 in my GMC the beginning of summer and it is still cooling great. The R4 comp is leaking some at the seal. I have a brand new --not rebuilt--comp that I'm going to have a friend install for me this winter and recharge it with 12.( He has a garage and owes me some favors) Last week I got two partial jugs of HotShot, along with a bunch of other misc stuff, from a guy who is retiring from a/c and ref service. I have never tried HotShot before, but have heard it is pretty good. Any comments welcome!