I turn on the AC in summer and the air gets really dry, even when a humidifier's running right next to it. Should I get something with a humidifying function instead of the air conditioner? Or is it just that they don't work together?
Just try not putting the humidifier right in the path of the air conditioner - place it at the opposite end of the room or in an adjacent room instead. The AC really does dry out the air (it's a side effect of cooling), but if the humidifier isn't fighting directly against its airflow and instead works in different areas, you'll notice the results more. And yeah, buying an air conditioner with a humidifying function is just marketing - those things work poorly because the physics doesn't change.
A dehumidifier will do way better than trying to fight the air conditioner with a humidifier :) Here's how an AC works: it cools the air, which causes moisture to condense and drain outside - so the air gets drier. A humidifier just adds moisture, but the AC removes it right away, so it's pointless. Instead of having these two devices battling each other, you could get an air conditioner with a dehumidifying function or install supply ventilation with humidification - they work together and don't interfere with each other.
The air conditioner is literally drying out the air - it's a side effect of cooling, and the humidifier just can't keep up with that kind of dehumidifying power. Instead of buying a new air conditioner with a humidifying function (which often doesn't work very well), it's easier to lower the temperature setting - the smaller the difference between outside and inside temperature, the weaker the dehumidifying effect, which means the humidifier will be able to do its job better.
The air conditioner is just stronger - it removes moisture as a side effect of cooling, and the humidifier can't add water faster than the AC pulls it out. It's not incompatibility, it's a difference in power: one dehumidifies 5 to 10 liters a day, the other barely handles one. Air conditioners with humidifying functions are often just marketing too - they don't do much of anything.
I had the same issue - I'd turn on the AC in the heat, and my lips would crack, my eyes would dry out. I bought a humidifier thinking it would help, but it barely made a difference. Then I figured out what was going on.
The air conditioner does dry out the air, but here's the key thing: it's not because it's actively "pulling out" moisture, but because cold air physically can't hold as much moisture as warm air. When it cools down the room, the humidity percentage drops sharply. And your humidifier just can't add water faster than the AC is "removing" it through condensation. It's not a question of power in the direct sense - it's thermodynamics.
Air conditioners with a humidifying function, by the way, are just a marketing gimmick. A regular AC unit can't cool and humidify at the same time by itself - that goes against how it works. Better to just accept that the air will be drier in summer, and either live with it or keep the AC from running at full blast. Or put the humidifier in the next room - it'll work better there since the water won't be immediately removed by the cold air flow.
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