They refuse to work on it because they dont have a way to start and run the ac unit, they only have 220v at their facility.
If they need to take the ac unit at their shop, let them take the 110 transformer you have so they can work on it.
If your tech/mechanic is refusing to work on a 110v running and connected ac at your place, fire him and hire a real mechanic. This one is probably a clown.