you have a humidity issue in your house or a leak at the airhadler
there are a couple of posibiltys that could be easy fixes and some hard ones if it is over sized for the house but it sounds to me like its sweating at the supply of the unit which could be just a small air leak, poor connection causing the problem you will have to take pictures or call them back for a look at what you have
once you think you've seen it all
I would rather work for free than be look upon as a thief!!!!!