For a 2-ton split-system A/C condensor, a 20 amp line should be sufficient. I say maybe because the 20 amps might only meet the minimum over current protection that is required. Whenever I run lines for an A/C circuit I prefer to meet the maximum OCP.
But to be on the safe side, I'd either find out for sure the requirements, or just run some 10-2 NM and be done with it.
Good luck.
