I'm struggling with humidity, too, here in the Pac NW with my grow room in the garage. So far I've managed some control with merely increased air flow. Have been trying to decide between a "real" dehumidifier (one with a compressor) or A/C and whether to treat just the room or the entire garage from which I'm drawing intake air (have 130 CFM of exhaust installed). The responses above concur with my conclusions... any A/C unit in the room will be too powerful and would be unusable in winter in my environment and thus wouldn't help with humidity. Like Hycheese, I'm looking at one of the small ($110-140) dehumidifiers. Not too big because it will add some heat to the room which I'm hoping my exhaust fans will handle. I may end having to have both, at least for the summer months. Like everything else so far with this grow room in the garage, it seems to take 2 opposing devices to recreate one ideal mother-nature environment.
Hope you'll let us know how the A/C works out for you? Is your room inside your house? That seems like it would be easier??