So about 1 month ago I finally finished my active service in the Marine Corps, and am looking to get back into HVAC. I have been completely out of the trade for the past 4 years, and it showed when I went in for a job interview last week and had to take a test. I really dont remember everything that I learned back when I graduated from tech school. Anyway, can anyone recommend a refresher course that is out there? I have heard that a lot has changed, but nobody really seems to want to tell me what has changed. Any help?