A HVAC RTU, or Heating, Ventilation, and Air Conditioning (HVAC) Rooftop Unit, is a self-contained system used to condition the air in a building. It is typically installed on the roof of a building and consists of an outdoor condensing unit, an indoor evaporator coil, and a fan. The condensing unit contains a compressor, condenser, and other components that work together to cool the air. The evaporator coil absorbs heat from the air and transfers it to the refrigerant, which is then circulated back to the condenser. The fan then blows the cooled air into the building. HVAC RTUs are used in a variety of applications, including residential, commercial, and industrial buildings. They are also used in some larger buildings, such as hospitals and office buildings, to provide air conditioning and ventilation. HVAC RTUs are a cost-effective way to provide cooling and ventilation in a building, and they are becoming increasingly popular as a way to reduce energy costs.