Well, air conditioning is not everywhere in Abyss, I think, is it? Also, Exador doesn’t think much about such things but pay attention to the carvings? The furnitures? The floor? Even the size of the room?
As for temperatures.
This might be a game of semantics, but near the boiling point of water, means a bit lower or [b]higher[/b] than the boiling point of water, you only take the lower end when you say about 190-200 F.
You also not quite correct in comparing the circumstances of outdoor escalators to the circumstances of the Abyssal escalators. For one, most of the time outdoor elevators aren’t exposed to heat. Half of the day is night and the highest temperature happens only for a few hours in midday. Early morning and twilight isn’t really that hot. In the Abyss, the hight temperature is constant.
Second, the heat often comes from the sun which only affects the surface of the escalators, not to mention many have roofing or is mounted on the ground which often is cooler than the surrounding. Not so in the Abyss.
As for humans existing in such temperatures… they should have died of heat stroke.
Now, the cooling runes should work but who, and how do they maintain the magic? As you say, very few demons know magic. Only a handful really. And they being high and mighty, I don’t think, they would be going allover the city checking the runes without an exuberant amount of payment.
As I say, this issue is really not justifiable. The circumstances just don’t make for it. It doesn’t matter much really. Many stories has such stuff (like superhero stories), and is often just hand waved, and readers just does’t mind. Just be careful, it may become stupid and absurd, just like the movie where Superman turns back time.