This would be a good time to take a look at the parts of a freezer. Now a freezer's really nothing but a large, insulated box with a heavy door and some bins and shelves inside, right? And all of this is connected to what is essentially a souped up air conditioning system.
Now the first part of this system is an electronic thermostat which monitors the temperature inside your freezer—usually the refrigerator, too. And I know, that's a thermometer. But I don't know how to draw a thermostat. There. Now this thermostat is connected via electronic wires to a device called a compressor, which is usually on the bottom or the top of the unit. And it's just a small, little device. Usually looks kind of like a tank. And it compresses what is called a refrigerant, usually R134A or something like that. Systems used to use ammonia, which is very, very dangerous. Anyway, it compresses it until it becomes extremely hot, and condenses into a liquid form. It's usually a gas in nature.
So it's so hot that the heat needs to be dissipated. So it goes through this big set of coils on the back of your unit. And it slowly gives off its heat, getting cooler and cooler all the time. But it's still a liquid, okay? And that is important, and it's under pressure, okay? Then, this coil basically punches through to your freezer, and the refrigerant goes through something called an expansion valve, which releases all of the pressure, and that makes the refrigerant immediately evaporate back into a vapor form. Well, this is called a phase change. And as this changing vapor moves through the coil inside the freezer, it absorbs a huge amount of heat from your food, thus freezing it. It's just that simple.