Most common refrigerators have four major parts to its refrigeration system -- a compressor, condenser, expansion valve, and evaporator. In the evaporator section, a refrigerant (up until very recently it has been vaporized, and heat is absorbed through the inside walls of the refrigerator, making it cold inside. The freon boils at -6.6 C (about 20 F) when pressurized at 35.7 pounds per square inch, so evaporator temperature is maintained at or near that temperature if the refrigerator is working properly. In the next stage, an electric motor runs a small piston or Wankel compressor (some new compressors are vane type) and the Freon is pressurized. This raises the temperature of the Freon. The resulting super-- heated, high-pressure gas (it is still a gas at this point) is then condensed to a liquid in an air-cooled condenser. On most refrigerators, the compressor is on the bottom and the condenser coils are on the rear of the refrigerator. From the condenser, the liquid Freon flows through an expansion valve, in which its pressure and temperature are reduced the conditions that are maintained in the evaporator. The whole process operated continuously, by transferring heat from the evaporator section (inside the refrigerator, to the condenser section (outside the refrigerator), by pumping the Freon continuously through the system described above. When the desired temperature is reached, the pump stops and so does the heat transfer. Freezers and air conditioners work exactly the same way. The difference is mostly in their compressor capacities and differing pressures.