As the Outside unit (or radiator) cools this hot vapor, it condenses into a liquid just like steam condenses into water when it loses its heat. This high-pressure freon liquid which has now had a lot of its original heat forced out of it, is then pulled back into the house where it waits its turn to pass through a tiny opening that is the entrance to the indoor coil that sits within your home’s air stream.
By using this tiny opening to “back-up” the pressure on the outdoor part of the system, it allows the compressor to maintain a low-pressure side within the indoor coil that is in your home’s air stream. When the cooled High-pressure gas finally passes into this low-pressure area, the difference in pressure causes part of it to immediately expand into a gas. In a sense, this is like the compressor working in reverse, because now the cool freon is occupying a bigger area, so the heat that was left in it now has to spread itself out over its bigger size.
This need to use its limited heat over a now bigger gas molecule, causes it to rapidly become quite cold so that as it passes through the indoor coil, the air passing over this coil (the radiator effect again) is cooled and then spread through your home by your home’s ductwork. Meanwhile, the heat that was taken out of your home’s air, has entered the warming freon gas so that when it gets back to the compressor the whole process is repeated.