While the space temperature in a refrigerated space may be used to control the refrigeration system, there is a lot more going on that we must also take control of. 

The thermostat initiates a pump down cycle to control/limit refrigerant migration to protect the compressor and enable defrost to occur more rapidly. 

Control over the temperature, humidity, velocity and direction of air leaving the unit cooler must be maintained to ensure that product is not dried out or frozen even when stored in temperatures above freezing. 

How product is placed within the cooler or freezer must be controlled so that sufficient airflow through the space and around the product occurs for quick and efficient heat removal.