As the effects of climate change on the environment become more prevalent, the steps to mitigate our negative impact become more urgent. Heating, ventilation, and air conditioning (HVAC) is a system used to maintain an optimal conditioned space based on a desired need. HVAC related electrical consumption plays a large part in the burning of fossil fuels. A proposed solution to reduce the amount of HVAC power consumption is a solar thermal contribution. The goal of this research project is to understand the effect caused by the addition of solar thermal energy to an HVAC system. At Marine Corps Air Station (MCAS) Miramar in San Diego, a conditioned space has been outfitted with an array of sensors to quantify the performance of the HVAC system. These sensors measure the various thermodynamic properties to develop a complete understanding of the system’s operation. The thermodynamic states of the air before and after the evaporator coil are used to determine the heat transfer rate. Monitoring the electrical draw of the compressor provided the work input the system. The coefficient of performance (COP) is the ratio between heat transfer and work. This method is used to determine the operational behavior of HVAC system before and after the solar thermal addition. The solar thermal addition is introduced by two evacuated tube collectors (ETC) placed on the roof adjacent to the conditioned space. The ETC’s were piped inline between the compressor outlet and the condenser inlet. The increased refrigerant temperature caused by the solar thermal addition increased the rate of heat transfer allowing the refrigerant to condense at a faster rate. The theory is that the increased condensing rate allows for the compressor to turn down, thus requiring less power. Baseline performance did not have a strong dependence on variations in cooling loads. The system with the solar thermal addition had a linear dependency on cooling loads, with the performance increasing as the cooling load increased. There was no discernible effect caused by an increase in solar insolation. To properly evaluate the legitimacy of this solar addition a larger cooling load range must be achieved.