The thing that comes to mind to most people when they think of air conditioning is just cold air coming from a register. This is not so. All need to be reminded that the term means that the air is filtered and then conditioned. Its the conditioning part that is overlooked by more then just a few. What I am getting at, is that the homeowner or technician should check for a fresh air intake when servicing the system. There should be a fresh supply of air introduced to the system using ductwork directly to intake side of the furnace. If the house is well sealed and no fresh air intake is installed, then all that is happening is circulation of stale air. For years, I complained to the serviceman about the comfort level and it appeared to be humidity related along with the smell of mildew. My homes humidity level was building up faster then the system could remove it. After I installed a fresh air supply using 4 inch duct, it made a big differance in the comfort level. For what its worth.