iii Pr eface This 20th edition incorporates many changes: • New technical updates include added informa- tion on variable refrigerant fl ow (VRF) systems, microchannel heat exchangers, variable frequency drives, thermostat diagnostics, HC and HFO refrigerants, and additional Code Alert features. New and updated content focusing on energy ef- fi ciency includes air-side economizers and multi- stage and zoning thermostats. • Over 400 new images and illustrations have been added throughout the textbook. • A new Careers and Certifi cation chapter and new Service Call Scenario features provide you with an overview of career opportunities available in the HVACR industry and an introduction to workplace skills that will help you succeed in your career goals. • A new Safety chapter provides an overview of safety-related topics to complement the strong, existing contextual safety information located throughout the chapters. In the coming years, the number of new positions in the HVACR industry combined with open posi- tions due to retirements is expected to be signifi cantly greater than the number of new employees entering the fi eld. This will create a shortage of trained workers and a surplus of employment opportunities. You are entering the HVACR fi eld at an ideal time, and Modern Refrigeration and Air Conditioning will be a fantastic resource for you as you build your career! Modern Refrigeration and Air Conditioning is the standard for a new generation of learner. This classic is an excellent blend of theory, skill develop- ment, and service techniques to help you learn how to install and service refrigeration and HVAC systems. Modern Refrigeration and Air Conditioning delivers comprehensive and authoritative content on the basic and advanced principles of refrigeration and air con- ditioning, provides excellent instruction and training in the skills and techniques essential for servicing and troubleshooting, and emphasizes career opportunities, workplace skills, and safety. The content in Modern Refrigeration and Air Conditioning is correlated to the curriculum guides and competencies used for HVAC Excellence and PAHRA program accreditation. The accreditation curriculum dovetails with entry-level and professional certifi ca- tion exam requirements. Thus, Modern Refrigeration and Air Conditioning is a valuable resource as you begin your journey toward entry-level certifi cation, employment, professional certifi cation, and career advancement. Modern Refrigeration and Air Conditioning has been carefully designed and crafted to make your learning experience effective and effi cient. Concepts are explained clearly and simply, with text narrative supported by numerous engaging and attractive illustrations. The preview and review features in each chapter—Chapter Outline, Technical Terms list, Review of Key Concepts, and Summary—help you quickly master HVACR concepts and topics.