Worldwide, approximately 25-30% of electricity is consumed by air conditioning and refrigeration systems therefore energy efficiencies of these systems are very important. Much research on HVAC should be performed in order to increase the efficiency of these systems. In this study, an air-to-air heat pump for cooling purposes using R404A was observed. The entropy generations of the elements of air-to-air heat pump were experimentally carried out in terms of surrounding air temperatures between 25°C to 30°C. In addition, a computer program was improved by means of Engineering Equation Solver (EES) for this purpose; temperatures, pressures, and the power delivered to the compressor and the blowers were also measured. As the surrounding air temperature increased, the entropy generation in the compressor, outdoor unit, and indoor unit increased while the entropy generation in the capillary tube decreased. The maximum entropy generation was obtained in the compressor. Entropy generation of the compressor increased from 0.003026 kW/K to 0.003172 kW/K.