A method for constructing a module of a modular cooling unit includes acquiring a plurality of tubes, each tube having a first end and a second end, and overmolding a first header onto the first ends of the plurality of tubes to form a watertight connection between the first header and the first ends of the plurality of tubes, the first header having a plurality of parallel first slots, each slot of the parallel first slots having an extended surface configured to receive and retain the first end of the tube.