There are many reasons you should only hire a licensed HVAC company to complete your maintenance, service calls, or installations, including insurance coverage, safety guidelines, quality of workmanship, and knowledge of local regulatory standards and building codes.
An unlicensed HVAC contractor typically will not carry insurance and has no authority regarding local building codes, safety, or standard guidelines. If they have not dedicated the time to become a licensed HVAC contractor, imagine the quality of work they will do.