Abstract: A device and method of operating a diaphragm pump having at least three chambers is used in a vapor compression refrigeration system. Each chamber contains a fluid having a different set of pressure and temperature characteristics. Adjacent chambers are separated by movable barriers, such as flexible diaphragms or pistons, that are sequentially moved by pressure changes resulting from heating and cooling the fluids. The fluids are chosen so that driving fluids operate in a substantially narrower temperature range than a working fluid but have the same operating pressure range permitting use of a thermal energy source having a selected temperature to power the pump. Optimal selection of both driving fluids and the working fluid permits use of a low grade heat source for thermal energy.