Some refrigerant gases can cause environmental damage. As a result, you need a certificate from the Environmental Protection Agency to work with them. In most states you also need a license.
In some training programs and many apprenticeships, you need to purchase your tools.
For information about apprenticeships and other training opportunities, call or visit your local contractors, union offices, apprenticeship agencies, or your nearest employment service office.
As HVAC technology continues to advance, you will need to keep your skills up-to-date. Expect to take classes throughout your career. Often manufacturers of HVAC equipment teach these courses. The good news is that usually you can expect your employer to pay for this training.