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.
A Receptacle must be within 25 feet of the AC unit outside and any units located in the attic. - 210.63
One light must be a located near the air handler located in an attic. The switch for the lighting outlet shall be at usual point of entry. – 210.70(A)(3)
The air handler located in the attic must have a disconnect means to turn power off to the air handler located near it.