If the ac is a 220v ac like 18000 btu or higher you have to wire it as 220v its a either 110v or 220v yes you can wire a 110v outlet as 220 but there is something to know first. It must be the only thing on that circuit so just because you want that outlet 220 doesnt mean its not wired to other outlets. Then you move the neutral over to your new breaker. If you are unsure or not clear ask an electrician yes it may cost you a little but better than saying OOPS later and having a fire.Can't I just wire it with a 30amp double pole breaker with #6/8 on 110? I'm under the impression that 208/230 has a range of voltage so at 220 would work fine?