This is useful info Westhamfan, I'm an air con engineer hopefully coming out in Jan, so I will certainly be taking your advice. As I've been through the process for skills approval OP, I would get the process underway pretty quickly as the vetassess process is quite long and drawn out. Also they only do a few skills assessments over here at the moment, I had to wait 6 months for mine and they tend to do the three trades on the same day - plumbing, electrical & air con.
So it could be as much as a year before you could get out there to work depending on vetassess.
If this is something you and your family are fully on board with, I'd say go for it, if the worst happened and you came back at least you'd be able to say you've done and you will always be able to work back here without too much hassle.
Good luck, whatever you decide!