Getting ice from the machine at work today and it got me thinking on how those things work and I thought I would share that with y'all in case you had wondered the same thing.
First of all the cooling system relies upon a gas. A modern fridge uses ammonia, older fridges used Freon (a Chloro-Flouro-Carbon, or CFC) So we moved from something that is dangerous to the atmosphere (CFC) to something that is dangerous to you. But it is more efficient so I guess that works. The system works like this, the gas flows thru the cooling tubes in the freezer (and fridge) then goes into a compressor which compresses it into a liquid before it goes out the tubes that are on the back of the fridge.
So how does that work? The gas runs thru the tubes and draws away heat from the compartment causing that compartment to be cooled. That gas then goes into the compressor. The compressor raises the pressure to put out liquid ammonia. But compressing the gas raises the temperature of the ammonia. So now it needs to be cooled off and this is done by sending it thru the coils on the back of the fridge.
The final stage is to get the ammonia cold again. This is accomplished by depressurizing the liquid so it can go back to gas again. The depressurization causes a temperature drop.
So: cold gas, pressurize (and heat) to liquid, bleed off heat then depressuize (and cool) to gas.