The objective of this work is to point out using a theoretical approach the influence of air, simplified in the form of nitrogen, when it is present inside the refrigeration system on its operational and functional parameters. Small vapor compression refrigeration systems are targeted. Mixtures of R600a and nitrogen are considered to have nitrogen mass fractions ranging from 0% to 0.5%. The thermodynamic properties of the mixtures have been determined by using REFPROP software. The mixtures behave as non-azeotropic fluid. Results point out a strong influence of the nitrogen presence on the operational and functional parameters of the refrigeration system. If the mass fraction of nitrogen increases from 0% to 0.5%, the condensing pressure increases with 139%, the compressor discharge temperature increases with 67%, the specific mechanical work input for the compressor increases by roughly 57% and the coefficient of performance in function decreases by 37%. Future work will focus on a more realistic approach based on constructive aspects of a small refrigeration system.