How does a refigerator work?
it has an evaporator in the fridge and it cools down the gasses and turns them into a liquid which is subzero and the the liquids cool down your food.
Defrosting is necessary to rid the cooling pipes of a refrigerator of ice formed over them. The thick crust of ice prevents the refrigerator from absorbing more heat from the refrigerator/freezer contents hence it needs to be defrosted so that the encrusted ice over the circulation pipes carrying the refrigerant can be melted away so that the refrigerator can work more efficiently.
Dense gas is pumped through small holes within a metal tube, by a motorized "compressor." When this gas makes contact with the metal on the inside, it has a cooling effect and the metal absorbs the heat from the air on the outside of the tube. Once the heat has been absorbed, this air is pumped in, or cycled through the fridge and freezer to keep things cold.