Re: Norcold Heater
The cooling process in an RV refrigerator works by absorption, and the coolant moves by convection flow and has no moving parts, pumps, or compressors.
What happens is that a mixture of ammonia & distilled water is heated in a boiler and it turns to a vapor. That vapor will rise to the very top of the refrigerator because hot vapor rises and cooler liquids flow down. The heater vapors are under pressure due to the absorbed heat. When it reaches the top of the refrigerator, it enters the cooling coils of the freezer first, and as the pressure is released the vapor expands and it also absorbs heat energy from the coils, thus lowering the temperature inside of the freezer compartment. The expanding vapor then flows down through the coils and enters the coils of the chill box part of the refrigerator. Any remaining vapor pressure then fully expands again absorbing more heat energy from the chill box as it slowly moves toward the heat exchanger.
In the heat exchanger, air moving upward through the back of the refrigerator cools the now low pressure vapor back into a liquid and it flows on down, into the liquid reservoir at the bottom of the refrigerator. From that reservoir the liquid runs into a boiler where either a propane flame or an electric heater supplies the heat to vaporize the mixture again and the pressurized vapor again rises to the top, due to convection because hot always rises. Since the most vapor reaches the freezer first, it also will cool first and if there isn't enough cooling, or if the freezer is too warm, all vapor pressure will be released in the freezer and so no effect is seen in the chill box until the freezer is fairly cool and no longer supplies enough energy to allow the vapor to completely expand.
The RV refrigerator is designed in that way for two reasons. First, it means that when cooling ability is limited, the frozen items will be protected most. Second, it also makes for much more simple controls since the designer just puts a thermistor on the cooling coils of the chill box which is then used to control the cooling operation. With this design, by using the proper ratio of cooling coil size the freezer will stay a proper temperature differential below that of the chill box and so one control does the job.
This is a pretty simplified explanation of how they work, but it should give you some idea of how you can use heat, to cool a refrigerator and even to freeze things. The key is that when a pressurized gas is allowed to expand it has to absorb heat energy, no matter what the surrounding temperatures may be. The heat that is removed in the expansion process is then removed from the refrigerator cooling unit in the coils at the very back of the flue area by the air that rises through the cooling unit and out the top vent. That is also the reason that the addition of a small fan to the rear of the refrigerator in hot weather can improve the cooling of the refrigerator, since excess heat has to be moved out the top of the refrigerator.
