A thermoelectric heating and cooling module was constructed for installation in a water to water air conditioning system aboard a submarine. This module has a cooling rating of 2550 BTUhr. at a coefficient of performance of 0.75 and an operating current of 35 amperes dc. This rating was based on a 85 F sink water temperature and a chill water temperature of 55 F. The unit was designed to withstand submergence pressures and the corrosive effect of sea water in all water passages. It occupies a volume 1 ft. by 1 ft. by 3 inches and was designed for ease in stacking into larger capacity units without additional space being required for coupling between units. It has a weight of 50 pounds.