15 or 20
(for some reason it did not like the way I made a chart earlier, so I had to edit to this version. I hope you understand it.)
Given all circumstances and ideal situations, the above chart gives the amp rating for all receptacles.
As stated earlier, the start up current draw on an A/C unit can be rather high.
On a 15 amp receptacle and 15 amp breaker, you can run the A/C for about 1 minute.
On a 15 amp receptacle and a 20 amp breaker, you can run the A/C, but nothing else should be ran such as a TV, toaster, hair dryer, radio etc....
Then obvisiously we can run the A/C and other accessories on a 30 amp circuit.
I would run the A/C on a 20 amp circuit and run it long enough to cool off the living area, but I would not run it all day or all weekend.
I hope this helps!!