On a hot, humid day my air conditioner does a good job of cooling the house but my basement is very, very cold causing condensation on the windows. None of the air vents are open in the basement.
How can I keep the basement from being so cold.

Insulate the ducts.

You may also want to tape or cover the basement vents,to keep any cold air from escaping into the basement,, and make sure the door going into the basement from the living quarters is kept shut