I studied this but can’t recall the exact details. In the past they used R-12 which required less pressure. It was banned because it was making a big hole in the Ozone layer.

I think we now use R-32 which is as good but requires more pressure. And that’s probably why new ACs are noisier.

nostr:npub1csamkk8zu67zl9z4wkp90a462v53q775aqn5q6xzjdkxnkvcpd7srtz4x9 probably knows these details.