An absorption chiller assembly (20) includes a low-stage generator (42) that utilizes heat from vapor resulting from operation of a high-stage generator (26) and heat from another hot liquid such as coolant fluid associated with a prime mover (22). An example low-stage generator (42) includes an arrangement of conduits for directing flow of the two heat sources through the low-stage generator in a manner that both sources simultaneously interact with a refrigerant solution within the low-stage generator. A disclosed example includes an integrated diverter valve that is preassembled and packaged within an absorption chiller assembly. A disclosed heating mode in one example includes using an absorber (60) and a condenser (56) for heating fluid useful for heating operations.