Did you verify the condenser coil was clean as alldodge suggested? Could be iced up and blocking off air flow. If it's icing up the problem could be lint build up acting as a wick to hold moisture then freeze. The other thing I'd check is routing of the duct to make sure it isn't kinked in any way, it's easy to bent the duct and choke off air flow. Verify the duct size is adequate for the AC unit. I had a Bayliner that had the wrong size (4" installed/6" required) and it was a factory installed option. Air intake grill want correct total area. Made major difference in air flow and cooling when I both were corrected. Blower wheel could have shifted away from blower inlet, they're typically held to the shaft with a ring clamp (not bolted or held with set screw) OR someone may have work near it and accidentally pushed it farther away OR natural center of blower motor may be pulling it away from the blower intake causing loss in pressure to produce design air flow.
