Patent ID: 8821651

Claim:
A method for surface treating a heat exchanger, comprising: (1) a pickling treatment step of causing an acidic cleaning agent to come into contact with a heat exchanger made of an aluminum material and vacuum brazed; (2) A chemical conversion treatment step of causing a zirconium-based chemical conversion treatment agent to come into contact with the aluminum material after the pickling treatment step; and (3) a hydrophilization treatment step of causing a hydrophilizing treatment agent to come into contact with the aluminum material after the chemical conversion treatment step, wherein the acidic cleaning agent contains nitric acid and sulfuric acid, and contains 0.01 to 5% by mass of a ferric salt, and wherein the hydrophilizing treatment agent contains silica grains coated by a vinyl alcohol polymer, and a polyallylamine resin, a total content of the silica grains and vinyl alcohol polymer being in the range of 0.2 to 25% by mass, a mass ratio of silica grains to vinyl alcohol polymer being in the range of 30:70 to 70:30, and a content of the polyallylamine resin being the range of 100 ppm to 5000 ppm.