SUBCOURSE OD1750 EDITION A REFRIGERATION AND AIR CONDITIONING IV (EQUIPMENT COOLING) REFRIGERATION AND AIR CONDITIONING IV (EQUIPMENT COOLING) Subcourse OD1750 Edition A United States Army Combined Arms Support Command Fort Lee, VA 23801-1809 14 Credit Hours INTRODUCTION This subcourse is the last of four subcourses devoted to basic instruction in refrigeration and air conditioning. The scope of this subcourse takes in unit components of the absorption system, including their functions and maintenance; water treatment methods and their relationship to centrifugal systems; centrifugal water pumps and electronic control systems, including the relationship of amplifier, bridge and discriminator circuits to electronic controls. The subcourse consists of.