Method for forming heat exchangers

A method for assembling and brazing a heat exchanger suitable for use in an automotive air conditioning or cooling system, wherein the heat exchanger has a plurality of tubes extending between a pair of headers, said method comprising the steps of:

• forming the headers and the tubes from an aluminum alloy material, each of the headers having a plurality of apertures corresponding in size and number to the plurality of tubes, each of the headers and tubes having corresponding surfaces which serve as pairs of joining surfaces therebetween;
• depositing a substantially nonaqueous flux-brazing composition on at least one of each of said pairs of joining surfaces, said flux-brazing composition being deposited in an amount sufficient to enhance brazeability and braze said pairs of joining surfaces during a brazing operation, said flux-brazing composition consisting essentially of from about 10 to about 50 weight percent of potassium tetrafluoroaluminate flux, from about 2 to about 13 weight percent silicon, from about 0.5 to about 3 weight percent of a metal selected from the group of zinc, copper, indium and tin, and from about 0.1 to about 2 weight percent hydroxypropyl cellulose, with the balance being aluminum;
• inserting each of the tubes into a corresponding one of said plurality of apertures in each of the headers so as to extend in hydraulic parallel between the headers, such that each of said joining surfaces of the headers are in intimate contact with a corresponding joining surface of the tubes, the headers and tubes forming an assembly;
• and
• brazing the plurality of tubes within said apertures of the headers by heating said assembly for a duration which is sufficient to melt the flux-brazing composition and thereby braze the tubes to the headers to form a monolithic heat exchanger;
• whereby said brazing step is effective to form leak-proof brazed joints at said joining surfaces so as to produce a leak-proof aluminum heat exchanger.