Been around a few units years ago when I worked in the hvac industry, when the compressor burns up and it gets hot enough to burn the Freon into phosgene gas you really want to stay away from that.
It kinda sucks if you know what you're doing but don't have a license that you can't even work on your own stuff.
Down here if you don't have a license you can't even go into the parts house and buy a capacitor.
I've been in the automotive industry since the early 90's. Once in the 90's I was working on a th350 transmission and a guy I worked with was asking me what this did and what that did I stopped working and said aren't you sae certified in transmissions and he said yes but all I did was read a book and take a test. That was when I said to myself I'm not going to worry about sae certification.