system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does my car need the aircon regassing every so often but my fridge/freezer never does?

As title really, I recently had my aircon regassed in my car but have had my freezer running constantly for 8 years, how come that never needs refilling?
gpt
A fridge refrigeration system is hermetically sealed, a car system isn't.

In a fridge, the compressor is attached to an electric motor, and then combined compressor/motor assembly is installed into a metal container, and the container is welded shut. There are special seals for the electrical wires to go in, but these are very strong and there is no movement on them. 

In a fridge, all the pipes are welded (actually brazed, but for the sake of simplicity let's ignore the difference) together and are welded to the compressor unit.

In a car, the compressor has to be attached to a pulley connected by a belt to the engine. This means that there has to be a moving seal where the pulley connects to the compressor. You'll never get a perfect seal where one part has to move, so a tiny amount of gas will leak out through this seal. As the seal ages, it will shrink and crack, so the leak will get faster with time. The compressor does have a bit of oil in it, and when you run the compressor the oil will splash on the seal and keep it moist. If you never use the air conditioning, then the compressor never runs, and the seal dries out and shrinks.

Also in a car, the system is designed for easy maintenance - so there are pipes and fittings that bolt together, instead of being welded/brazed. When these get vibrated on roads, then tiny amounts of gas can leak out when the vibration causes them to move slightly. 

Some new models of car (especially hybrids) use a welded-shut electrical compressor for the AC, instead of a pulley driven one, specifically to try to reduce leaks.