You can start by having the blowers/ airhandler cleaned out and properly checked. I'm all too aware of today's OA requirements, which at 15 cfm/ person can add a large latent load on the system. The 4 ton sounds too small for the application, as it should be a staged system also to provide humidity removal. We also put sensors on our systems to open the O/a dampers only when the rooms were occupied....we used motion detectors w/ a time delay board.
If everything was always done "by the book"....the book would never change.