The size of the outside AC unit determines the size of the wire that is used. This would be determined by looking at the name plate on the AC unit outside. The larger the tons, the larger the wire size and breaker. Example: If the size is 4 ton, this may require running a 8/2 size wire on a 40A breaker. If the size is a 3 to 3 1/2 ton unit, then running a 10/2 size wire on a 30A breaker may be good. The AC unit requires a disconnect near it.
