start with basic electricity...there more work then people to do it...
Go to the library and see if they have a copy of the book Modern heating and air conditioning or buy a used copy for $5 online. It will be the best money you ever spent:http://www.alibris.com/search/books/qwork/4425535/used/Modern%20refrigeration%20and%20air%20conditioning
The guide tells how to diagnose and remedy HVAC problems
If your a appliance technician now and had a chance to start over would you pick a different career or would you stick with appliance repair?
According to Ice, they don't hire fat guys either...right Bob?