It may seems confusing that liquid propane (LP) fuel used for heating can also be used to keep items cold. Though counter-intuitive, this process is commonly used for refrigerators installed in recreational vehicles and some homes.
Refrigerators that can operate using either LP or electric power work by using "continuous absorption." This method relies on small amounts of heat from either source and operates without complicated moving parts. When the refrigerator is in propane mode, LP fuel ignited in a burner provides the necessary heat. If the user switches to electric mode, the propane burner shuts down and an electric element provides heat instead.
Heat from either the LP propane or electric element is focused on the boiler, which contains ammonia. When heated to high enough levels, ammonia bubbles begin to form and are siphoned into a pipe. Constant heat creates a continuous flow of ammonia vapor through the pipe.
The vapor moves through an a device that forces the ammonia to evaporate. Because all evaporation causes cooling, the process draws heat away from the main storage area of the refrigerator.
Evaporated ammonia next moves through an absorber. Here, the ammonia is re-absorbed into the boiler where it first left. This re-absorption completes the cycle, and the substance is ready to be heated once again. Because there are no moving parts, gravity is used to help the cycle flow continuously.
Heat is created whenever the boiler is operating. To prevent this heat from interfering with refrigeration, metal radiators constantly dissipate it into the surrounding air. The cooling effect created by ammonia evaporation is focused on the insulated area where food is stored.