In this paper, the influence of moisture contained in the air on the cooling effect of the heat pump is demonstrated. The introductory part of the paper explains the influence of air moisture content on the operation of air conditioning systems, describes the associated heat and mass transfer during humid air cooling, and demonstrates how to use the humid air diagram used in practice. At the end of the introductory part, a technical description of the existing laboratory air conditioning system is given together with the associated equipment. In the practical part of the final paper, the results of measuring the operating parameters of the laboratory air conditioning system are presented. The results obtained by the measurement are graphically presented in the "Mollier" diagram for humid air, and the corresponding calculations were performed for the purpose of processing the measurement results. The calculation demonstrates the influence of the moisture content in the air on the ratio of the changed sensible and latent heat during the process of cooling and dehumidifying the air in the room.