Abstract: An adhesive supply unit for melting solid and quasi/solid materials, such as polyurethane (PUR) and other hot melt adhesives, is disclosed. The unit features an air control system that automatically starts, when the hopper lid is closed, to remove moisture from the moisture laden air in the hopper interior by alternately applying a vacuum to the hopper interior and then replacing the air with plant air that has passed through a series of dryers and filters. The dryers/filters, valving mechanisms and tubing are mounted directly to the machine body with a panel bolted to the machine, eliminating the need for storing the air control system on a separate cart. A sensor verifies that the hopper lid is securely closed before automatically initiating the drying/purging cycles which are repeated a number of times to assure appropriate dehumidification of air to acceptable levels.