Bruce makes some good points. First, try to idententiby any sources of excess moisture. Do you have a damp crawlspace thanks to El Nino? If there isn't any excess moisture source, there are a couple of possiblities related to the AC. First, it may be oversized. The amount of water it can remove is related to how long it runs, and an over sized unit will run in short bursts; the house gets cool, but moisture remains. Another possibility is duct leakage. If the return ducts run through unconditioned areas (as they usually do) and leak, they will suck warm humid air in not only reducing efficiency, but leaving more moisture in the air, not to mention driving moist air into the walls and ceilings (very bad for the house). If there a supply duct leaks, they will tend to depressurize the house and suck outside air in through various cracks and crevices. To quantitativly assess duct leakage you need someone with the right tools i.e. a Duct Blaster, but you can get some idea of what the situation is by doing a "front door test". Rather than describe it here, go over to www.weatherization.com. Lastly, you may want to consider dual closeable returns for the room, one high and one low. Use the high one in cooling season, and the low one in heating season. Some food for though anyway.