Abstract: An improved method for assembling a brazed heat exchanger unit suitable for use in an automobile air conditioning system. Prior to assembly, a sufficiently viscous flux-brazing composition is selectively applied to the internal and external features of the heat exchanger which serve as the joining surfaces of the heat exchanger. The flux-brazing composition is specifically applied to the internal surfaces of the aluminum alloy header and the external surfaces of the tubes so as to form uniformly and consistently brazed internal and external joints. The flux-brazing composition of this invention consists of potassium tetrafluoroaluminate particles, an aluminum-silicon powder, zinc and a binder. The flux-brazing composition enables the selective application of both a flux compound and a brazing compound, eliminating excessive use of flux and eliminating the need to clad the components of the heat exchanger with an aluminum alloy brazing material.