This may sound a bit crazy, but if you tear down a machine and put it back together again, it is invaluable the knowledge you will gain. If you have a machine where you can do that, video it so you don't end up with a pile of parts and not know how to put it back together again.
Or remove a part, put it back, remove another part, put it back and so on. You will learn how the machine operates in this fashion. With the exception of some touch and go when I first started, hands-on self-teaching is how I went and probably how most do it.
As for the refrigeration side, I have had some formal instruction/training and that is just about all that I need. I do have mechs/validators sent off for service/repair as I'm not interested in learning how to fix those and don't have the time to do so.