I wouldn't advise anyone to start into the major appliance field these days. The appliances are getting harder and harder to service due to cheap designs or assembly methods and some aren't designed to be serviced at all. Also, with all the electronics being designed into them, sometimes it's just a guessing game which component is even responsible for a problem.
Manufacturers also don't want to pay much for warranty service so you'd have a hard time making a living working for them as well. It is also difficult to get service information unless you're affiliated with a manufacturer's service network. Catch 22.
Maybe you should look into the HVAC industry instead?