Adam . I doubt you can mix it. Take your vehicle to a a/c service center and have them reclaim the R-12 . You want to remove any existing freon slowly so it doesn't carry the oil out with it . Maybe a shop will do it for free since your giving them the freon? Pulling a vacuum is needed to remove any moisture that will freeze up and clog internal components till it thaws again. If you install the Maxfrig , let us know how it performs . Specs advertized sound almost too good to be true. I'd like to try it myself , but I imagine most shops are going to try to talk you out of it