The refrigeration load and capacity of the system fluctuates due to input conditions and change in ambient conditions. Since the capacity of the system is designed for maximum load conditions. During half load conditions, the capacity of the system is greater than the requirement. Hence it is necessary to control the capacity of the system to reduce the energy consumption and maintain the required design conditions. Automatic controls make the system to operate independently without skilled supervision and also maintain higher degree of accuracy in maintain the temperatures. The controls used in refrigeration and air conditioning systems are the devices that protect the various components of the system. The controls may be manually operated, electrically operated, electronically operated, pressure operated, temperature operated or pneumatically operated. The control system is the collection of many control devices. The control system has following elements: Control Variable, Controller, Source of power, Control device, Control agent and Processes plant.