In my opinion(you will find is differant than most)is you would be better off than most starting this trade. You have alot of the skill set already. The only hold up would be the refrigeration process.You will have to learn alot about plumbing/pipe fitting of most types of piping.Brazing/soldering.And being you dont have to learn all about electricity and controll function will leave more time to learn this very important skill. I would hire someone like you before a green man out of trade school.because you should have the basic skills and electrical safety. Just be ready for alot of after hours work. oh yea if your thinking residential be ready for some low crawling!PS there is alot I didnt cover but you should be ok just learn all you can and open your mind. Just stay positive and work hard and you will be fine, Also this is great place to learn for newbies, Get pro status as this will problably help you a great deal.Welcome to the most challenging and rewarding trade there is.