This paper presents the modelization of heat and mass transfer in cubical reactor of solar adsorption cooling machine. The reactor is heated by solar energy and contains a porous medium constituted of activated carbon reacting by adsorption with ammonia. From real solar data, the model computes the performances of the machine and shows the existence of the optimal dimensioning of the reactor. For the resolution of the equations describing the coupling between heat and mass transfer, we have adapted a “Boubnov-Galerkin” method combined to an iterative process, this method provides a continuous distribution of the temperature and adsorbed mass. The convergence of the method is discussed and the numerical results are compared with the results provided by finite-difference method. Considering the rapidity of convergence and the order of Algebraic system (That is generally inferior to 10), the proposed method appeared to be very effective in solving such problem.