by www.rversonline.org
It is a fact of nature, science, and engineering that when a gas is allowed to expand, it loses heat (cools off). Sometimes this can be seen after a well-chilled bottle of beer or pop is opened and ice forms inside the neck. In humid climates, on a cool morning, a gas station air hose will ice up as the tip is hissing — the same for air escaping out of a tire after the valve has been removed.
Some gases do this better than others: We are familiar with freon, but did you know that ammonia is quite a bit more “efficient”? The ammonia you buy in a bottle is in “solution” (water) — real ammonia is a gas.
To get these gases to “cool” first it is necessary to build them up to high pressure, and then bleed them slowly into a radiator. But “compressing” a gas heats it up! In order for a gas to “cool” properly, that heat build-up must be gotten rid of before it is bled into the cooling radiator. Home and motor vehicle air conditioners have a powerful compressor that imparts several hundred pounds of pressure to the gas, then it sent to that radiator looking thing in front of your RV’s coolant radiator where a flow of air gets rid of the heat. After that, the compressed gas is sent to the cooling radiator where a fan blows nice cool air out of the ductwork.
An RV refrigerator uses a propane flame to “compress” a special ammonia hydrogen gas inside the tubes. Actually the gas is heated which dramatically raises its pressure. Here comes another law of physics — hot gases rise and cool gasses come down. Sort of like in an automobile air conditioner, the hot compressed refrigerator gas is sent to a “radiator” where excess heat is gotten rid of and then the cooled compressed gas gets sent (by gravity) to the cooling radiator whose fins are inside the box. Who cares how gas is compressed, right? Once it’s compressed and the heat is taken away it’s ready to be expanded and deliver some chilly temperatures.
Large buildings use a form of “RV refrigeration” called “Chillers”. Some are the size of a railroad switch engine, and steam from a nearby boiler heats “lithium bromide” much like the ammonia hydrogen mix in an RV refrigerator. Then the heated lithium bromide is sent to a special radiator (sound familiar?) where excess heat is removed. In this case, the lithium bromide is not sent to distant radiators but instead transfers it’s the low temperature to circulating water, and that is sent to distant radiators.