The sealed system consists of a compressor, evaporator, condenser, tubing, filter-drier, and an accumulator. The illustration below is a rear view of a frost-free refrigerator. The evaporator is accessible from the front, and the compressor, condenser, and the condenser fan are accessible when the rear cover panel is removed (it is retained by a few screws). The upper part of the drain system has a small heating element (not shown) to prevent restriction by an ice buildup during the defrost cycle. The front grille is retained by screws or spring clips.
The cabinet, or body of the refrigerator, contains and supports the evaporator, condenser, and the compressor. The evaporator is located inside the freezer compartment where it absorbs heat from the food. This heat is transferred to the condenser where it is radiated to the outside air. The condenser is usually mounted at the back of the unit or in base of the cabinet next to the compressor (figs. 3 and 4). The air in a refrigeration unit is very dry because the moisture in the cabinet tends to collect and condense on the evaporator surface where the temperature is very low. That is why food should be covered with a moisture-proof cover to be kept from drying out.
The temperature inside the fresh-food cabinet ranges between 33°F and 42°F, while the temperature in the freezer section is between 0°F and 10°F.
Manual defrost systems are not limited to residential units. There are some commercial units that operate on the same principle, but mostly where temperatures range between 35°F-50°F.
Generally, the lower the temperature, the longer the food can be preserved.
The walls of freezers and refrigerators contain an insulating material to prevent the loss of cold air and to keep heat from penetrating. Either urethane foam or fiberglass is used as insulation in almost all units. In some commercial and industrial units, other materials may be used as well.
The walls of refrigeration units are made of cold rolled steel and are welded together. In a simple fresh – food refrigerator, the evaporator is located in the top of the cabinet and cold air is distributed automatically because cold air is heavy and flows down from the evaporator surface and settles on the bottom of the cabinet (see fig. 5). In frost-free refrigerators, cold air from the evaporator is forced into the fresh-food compartment by means of a fan because the evaporator and fresh-food compartment are separated by a wall. More about this later. (See fig. 6).