The paper presents research on scale formation performed in a laboratory model of an evaporative cooler. Such type heat exchangers are often applied in industrial cooling systems. As a heat carrier they usually use raw water, which despite its numerous advantages is also a source of many problems like corrosion and incrustation. The elaborated model makes possible to perform qualitative and quantitative testing of crystalline deposits that form on heating surfaces. The following tests performed with the application of the mentioned cooler model have been presented in the paper: 1. phase crystallization of calcium carbonate, 2. ammonium sulfate effect on incrustation in a model heal exchanger. Diffractometric tests have shown differences in phase composition of calcium carbonate deposits, which have formed at different temperatures and in the presence of ammonium sulfate. At 400C calcium carbonate has formed as anhydrous calcite and monohydrate while at 55-600C additionally as aragonite. An addition of ammonium sulfate has inhibited scale accretion and even caused its insignificant dissolution.