Abstract: An improved method for assembly of a brazed condenser unit for use in an automobile air conditioning system is provided which significantly reduced the defective rate due to leaky internal joints within the condenser. A sufficiently viscous flux composition is applied to the internal features of the condenser during assembly. The flux composition is specifically applied to surfaces of the aluminum alloy header which is clad internally with the brazing alloy, so as to promote complete and consistent brazing of the internal tubes and components. The brazing flux composition of this invention consists of potassium fluoaluminate particles in a liquid carrier consisting of a polyhydric alcohol, e.g., propylene glycol, and minimal amounts of water. This flux composition has a sufficiently high viscosity so as to permit its easy, consistent deposition on the header surface without subsequent displacement during assembly and processing.