I have a semi-cylindrical box stuck on the wall near the ceiling in my bedrooms. They each, when in operation (and thus with the vent open) has a small set of radiator fins visible. Each has a pipe that goes out through a hole in the exterior wall. On the outside is mounted a larger box that has a large fan, a compressor, and a larger set of radiator fins. In the summer they cool. In the winter they heat.

In the living room I have a large stand-up cabinet in place of the thing stuck on the wall. It otherwise performs the same task, with a (larger) pipe going out to a (larger) box with a compressor.

Is this what you're talking about?

[–] ReasonablePea@sh.itjust.works 2 points 17 hours ago

Yup, that compressor and tubing and fins is describing a refrigeration cycle. In the summer you are using it like a traditional AC where it soaking heat in your mini split and sending it out to the heat exchanger outside built around your compressor to dump that heat in a hotter environment than inside your house (amazing I know!) due to the change in properties of the refrigerant when compressed (or expanded). This process is effectively reversed in the winter to take energy which exists in the cold outside air and pulls it in to your house by expanding it outside. Compressing or expanding the refrigerant effectively makes it colder or warmer (whatever is advantageous for the situation) to be able to extract or dump heat into it.