My car runs lousy when the A/C is on?

My 2008 Kia Rondo LXV6 runs lousy when the A/C is on by normally when it is off. When I say it runs lousy I mean that is lags off the line and hiccups at low speeds. I know enough about cars to think this could be caused by a vacuum leak, but to be honest I am not entirely sure what that means, how to test it, or how to fix it. I know I am under factory warranty, but the closest dealership is a ways away they always try to sell me stuff I don't need. Any help would be appreciated.