Abstract: The invention is an improvement in a thermal stress screening system of the type using a single type of liquid for alternately transferring heat to and from the product. In the improvement, the product is confined in a single chamber during alternate heat transfer. That is, the system provides "one chamber" thermal stress screening. The system includes a plurality of tanks, one each for hot and cold liquid, and a heat exchanger associated with each tank so that the liquid in a tank is maintained at the proper temperature for stress screening. An improved method for thermally stress screening products, e.g., printed circuit boards, includes the steps of placing the product in a chamber, flowing cold liquid into the chamber, draining the cold liquid from the chamber and flowing hot liquid into the same chamber.