I would like to ask about the license to work in HVACR in USA.And the regulations for that.thanks?

Answer 1

You have a few approaches to this.
(1) You work for someone and in time learn and take the test.
(2) You can take courses and take the test. BUT, to work on your on you work for someone to get the experience.
This the easiest way to explain. It like an Electricians License. You have to work as an Apprentice and in time you can be your own Boss. But, you have to run the "Gauntlet" first.
Real-estate a good example I can explain easier. You take a class as you need certain training before you can take a test. See #1 and #2. You can take the test and get a license to sell Houses, but, you have to work for a Broker! After a certain amount of time you can take the Brokers Test and be your own Boss.