Introduction: Life changed immensely in the 20th century as air conditioning and refrigeration systems became more efficient and controllable. Air conditioning and refrigeration play an important role in ensuring human comfort, food processing, storage and many other industrial processes. We chose this topic because our life would be difficult without air conditioning and refrigeration. This article will talk about the history of air conditioning and refrigeration, the role of engineers in designing and building them, the lives of people before and after air conditioning and refrigeration, and finally applications in the area of ​​future achievements and developments. The history of air conditioning and refrigeration: Before the 20th century, most efforts were ineffective and people tried many things to provide cool comfort, until Leonardo Da Vince designed a mechanical fan and it was used in industrial environments . Then, an engineer named Stuart Cramer, likes the idea of ​​the latest heat and humidity control system and improves it and calls it "air conditioning" in 1906. A year later, air conditioning equipment was installed 'air designed by Witten Meier. in cinemas and hotels. And in 1927, General Electric introduced the first mass-produced refrigerator with a completely sealed refrigeration system and was one of a kind. By 1927, these improvements continued to progress and engineers completed research and developed air conditioning and refrigeration to consume less energy. Role of Engineers: The main job of engineers is to solve problems and design things that make people's lives easier. One of the problems refrigeration engineers faced in the early 20th century was how to transform the gas phase into the liquid phase. Therefore, heat will be released from the condenser. Additionally, the condenser takes care of rejecting heat from the system and does not change the pressure, so the pressure will remain high. • Third, the liquid will enter the expansion valve with the higher pressure and exit with the low pressure. • Finally, the liquid moves to the evaporator, where the heat from the internal air is absorbed and transforms it from a liquid gas. Subsequently we move again to the compressor, where the entire cycle is repeated. Compressors used in refrigerators use titanium turbines. Using titanium requires a high level of energy, which increases costs. One of the future technologies that will help save energy and reduce costs is the refrigerant known as “R-718” or “Water Vapor”. R718 can be more efficient than our current refrigerants.