When Mrs. Rastahomie says she’d too cold, I tell her to turn the air conditioner down.
However, to say “turn it down” implies turning the thermostat down to a lower temperature, thus making it colder.
However, to say “turn it up” implies increasing the air conditioner’s energy output, thereby making it colder.
It’s a conundrum, no? What should I say?
The eternal question. . . i always go with temperature rather than level of air output, because most of the air systems i mess with are programmed to respond to temperature readings. So if it’s too cold, i say, “Turn it up.”
Turn it off?
We must speak so as to be clear at all times:
“Dearest, my phalanges are frigid. Please make it less cold in our domicile.”
I use the same method at jkbelle. Numbers are so much more accurate 
Depends on the context. We generally speak of turning down the AC whether we are too hot or too cold, and the context is the key.
“Honey, you look so cute when you’re cold. Can we snuggle?”
She has to be told this? She wouldn’t have been able to come up with the idea on her own?
Seriously, what you said makes perfect sense to me. Except, what if there’s more than one knob on the AC? Like a blower control and a thermostat? Which knob do you mean to turn?
Great–now you’ve got a They Might Be Giants song running through my head. “Turn it up, turn it down…”
We have struggled with this issue for years. To me, it is perfectly understandable (and may be to Mrs. Rasta too): “Turn up the AC” means “make it colder” just as “turn up the heat” means “make it hotter.” Just subsitute the word “crank” – “Crank up that AC!!” See, makes sense!
“Turn down the AC” means turn the machinery down – so down that it goes off. “Turn down the heat” means the same thing; it’s only coincidental that we’re also talking temperature-wise.
Then again, maybe I’m the only one who thinks this way! Because hubby always says, “well, if I turn down the air, it’ll only get colder!” See, we’ve only been married 15 years. We’re still workin’ on that communication thing.
To make it less cold, one would turn down the AC, or turn up the thermostat/temperature.
Like Ellen Cherry, I am up the crank-it-up persuasion.