Frequent door opening/closing or lasting door opening time will cause the increase of energy consumption for refrigerators/freezers. To reduce the thermal load from ambient enhancement, the fan motor of evaporator could be set to stop to prevent cold air from leaking out by using a detection signal of spring relay as the refrigerator/freezer door opening. However, natural convection and thermal radiation cannot be avoided for a huge temperature difference between the food compartment and the ambient. Some advanced design with an air curtain is embedded on the top edge of refrigerator/freezer, so that ambient warm air intruding effect could be reduced by force circulation as the door opening. Thus, temperature rise inside the food compartment will be controlled. When door is closed, proper design with increased air circulating rate across the evaporator will improve the uniformity to be good for food preservation.