Liking to enter trade

Hello, I am looking to enter the hvac trade. I contacted the local union where I live and they gave me a list of contractors to reach out to about sponsorship but When I contact them no one calls or emails me back.

This would be new for me as I have been working in the medical field and would be switching careers. I am new to this but I have a good work ethic from my time in the military and I am eager to learn.

Do companies really give new people a chance or do they just want someone with at least time in the trade to not train as much? Or what can I do to help my chances ?

Ant tips or advice is welcomed and appreciated, thanks.