By the time I decided to start writing this book, I had worked in the HVAC & R industry for more than forty-five years. In this span of time, I had worked as a service technician in an NYC service company and as a trade instructor in several schools (see profile). I had written books and works; among them are RAC & E test-books, preparation for the EPAs certification, and the RMO's License for the NYC Fire Department, which had been used in the schools in which I worked. Regardless of the years that had passed, the refrigeration system used in Air Conditioning, systems as well as in Commercial Refrigeration, Domestic Refrigeration, etc., and in the equipment in general used today contains the same mechanical-electrical components as then.