Did the Freon AC units of the 50s dry out air like modern ones do, and if so why?

Question

I read an article today that said that modern AC units require a dryer built into them as HFC refrigerants like R-134a absorb water, whereas old Freon AC units did not require a dryer. Does this mean that AC units from the 50s did not dry out the air like modern ones do?

In: Physics

Answer 1

As others have said, these are two different things. I’ll try an ELI5.

Imagine a glass of iced tea sitting outside on a hot day. It’ll get drops of water on the outside of the glass. That water is called condensation.

Now imagine a glass of ice water sitting outside on a hot day. It’ll get drops of water (condensation) too.

Now imagine a glass of iced soda sitting … you get the idea. Same thing. All three glasses get water on the outside. Not because of exactly what is inside them, but because they are cold. And when moist air gets cold, it gives up some of it moisture. That’s just how air works.

So older AC units dried out the air, just like modern ones do, because they made the air cold, just like modern ones do. They used a different thing inside the AC unit (different type of refrigerant, see below), but they still made the air cold, so they still made the air dryer.

Now, what are dryers for? They’re not for the air. They’re for something else.

Inside your AC are special pipes through which a substance called a “refrigerant” flows. This refrigerant is the special sauce that actually makes the AC work. Describing that is a little beyond ELI5 (although I’m sure someone could do a decent job of it if OP is interested). Setting aside HOW it works, one important thing is the the refrigerant gets pumped into these special pipes, and then the pipes get closed forever (or at least until there’s a leak or something and the system needs more refrigerant).

Problem is, the world is a messy place and it is really hard to not let any water at all into these special pipes while you’re working on the AC unit (or that maybe rode in with the new refrigerant, or whatever). And water in these special pipes is bad for a variety of reasons. So the dryer sucks up any water that snuck in, so that everything keeps working happily.

Depending on what kind of refrigerant your AC uses, this may be more or less of a problem, so that’s why the type of refrigerant may matter. But it is still a thing, regardless.