Abstract: An environmental chamber for providing thermal stress screening is comprised of a plurality of modular components which may be quickly assembled and disassembled for ease of maintenance and repair. In particular, a heater/cooling unit is coupled by means of a plurality of quick release lockable fasteners to a plenum module. The plenum module in turn is coupled by means of additional quick release lockable fasteners to a blower module. The plenum module in turn is comprised of a heater plenum which communicates with a blower plenum. Gas is drawn into the heater plenum and passed over heating coils which are disposed into the heating plenum from the heating/cooling module. The gas is then communicated to a blower plenum. Cryogenic nitrogen gas is constantly bled through a small (0.015") hole of the liquid nitrogen valve body and is selectively provided to the blower plenum from the heating/cooling module.