This happens with me many times. And people misinterpret it. But then I thought for a while and now think that I should have some unambiguous sentence to convey my message.

Could you decrease the AC please?
Sure, why not.
Fifteen minutes later - Hey, it is chilling. Didn't you lower down the AC?
I certainly did. It was 22 degrees and I made it 18!
Ah, I mean decrease - make it less effective/intensive. The AC was too much.

Does increasing AC (Air Conditioning) means moving the degrees from 18 to 22 or 22 to 18? Both are right! The former is increase in AC as it's increasing in temperature and the latter one is correct in a way that it increased the intensity (like, increase the volume, it's not audible).

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    Yes, I hate it when they install the thermostat too close to the floor!
    – oerkelens
    Apr 1, 2014 at 9:28
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    "Turn down the AC" = "turn down the intensity of the A/C" (and therefore raise the temperature). Of course, there's still some room for misinterpretation, but you can fix that problem by setting the context. It's too cold in here; would you turn down the A/C? Problem solved.
    – J.R.
    Apr 1, 2014 at 9:37
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    @Happy you certainly can reduce/increase AC. That's because a washing machine or a refrigerator are the appliances, here, AC also means air conditioning!
    – Maulik V
    Apr 1, 2014 at 10:14
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    @Happy Except that most air conditioning units do not have customer-accessible controls to set the humidity, fan speed, or level of pollen filtering. They just have a temperature dial. So if someone says "please reduce the AC", the only thing the other person can realistically do is change the temperature setting. If you were speaking to the HVAC technician, more specific instructions might be called for.
    – Jay
    Apr 1, 2014 at 16:05
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    @Happy (a) Easier to just say raise or lower the thermostat and avoid the ambiguity: Sure. (b) AC's have other controls, like fan speed: Well, my home's AC doesn't. I can turn it on or off, turn the fan to "auto" or "always on", and set the thermostat. That's it, and every house I've ever lived in, that's been it. Maybe wherever you live or the kinds of AC units you get are different. Well, I'm thinking of central air. Window AC units often have a fan speed.
    – Jay
    Apr 2, 2014 at 13:19

2 Answers 2


The problem is of course that we are more used to heating systems than to cooling systems (heating is much easier, and humans have been doing it for tens of thousands of years).

And with every heating system, turning up the system means increasing the resulting temperature.

Many A/C systems have a temperature indication, and many even have buttons to increase or decrease the temperature. So effectively, when you mean "please decrease the effectiveness of the A/C", you are asking someone to press the up-arrow key on the A/C, increasing the temperature.

This is an contradictory thing for many people. When I turn up the heating, I increase the temperature. Now you want me to turn up the A/C, then I will likewise increase the temperature.

Strictly speaking, your interpretation makes sense (and as a stickler for literal interpretation, I have used it myself!). For most people, however, "turning up" any appliance that controls temperature means adjusting it in such a way that the temperature will increase.

There are examples where people mean the opposite of what they really say. Maybe the most common example is the confusing fact that electrical current runs in the opposite direction of the movement of the electrons.

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    A related example would be, "The milk is too warm, we need to turn ___ the refrigerator." Turn up, or turn down? Truth be told, I'm not sure which I'd say, particularly if the appliance had a knob like this, where a higher number means a colder setting. Ovens are so much easier!
    – J.R.
    Apr 1, 2014 at 9:44
  • "The problem is of course that we are more used to heating systems than to cooling systems". Don't generalize to all humans based on your observations which seem to restricted to humans in the "cold countries". In a tropical country, such as the place where I live, cooling systems are much more common, and there is hardly ever any need for heating systems. People here who don't watch American movies, etc. don't even know about such systems.
    – Masked Man
    Apr 1, 2014 at 12:16
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    @Happy: even so, heating systems have been used by humans for tens of thousands of years longer than any adjustable cooling systems. I am well aware that there are many places where cooling systems are used now and where heating systems were never used much for rooms, but even there, heating systems have been used to prepare food. And if you increase your fire, the temperature in your oven or on your stove goes up, not down.
    – oerkelens
    Apr 1, 2014 at 12:51
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    My point is that in all systems that we can think of "turning up or down" that regulate temperature, since before ewe started writing, "turning up" the appliance meant an increase in temperature. With the very very modern advent of cooling appliances, we find ourselves struggling with "turning up" resulting in the opposite effect. I think it has very much to do with this question, since the question illustrates exactly that confusion. Everything that regulates temperature will create a higher temperature when turned up... oh noes, new inventions now!
    – oerkelens
    Apr 1, 2014 at 13:04
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    I don't think the up/down issue requires extensive historical and psychological analysis. With a home heating system or an oven, you can interpret "turn it up" to mean "increase the temperature" or "increase the amount of work the appliance is doing", and the final result is the same. But for a cooling device, "increase the temperature" and "increase the amount of work it's doing" have opposite effects. So no ambiguity comes up in the first case but an ambiguity does come up in the second case. If we lived on a planet where no one ever invented home heating units or stoves, I think we'd ...
    – Jay
    Apr 1, 2014 at 16:10

With a heating system, an oven, a fan, water flow, etc. to turn up or increase or crank up the setting is unambiguous -- you want more of whatever the thing is doing, which means raising the temperature or flow. To turn down or decrease the setting reduces activity (leading to a lower temperature, etc.).

With a cooling system, it is potentially ambiguous, as the usual meaning is still to increase the activity, but the result is to lower the temperature. Thus the convention (at least in the US) is "turn up the A/C" means to make it colder (lower temperature) by increasing the work the A/C unit is doing. In other countries and cultures, it could certainly instead mean "raise the temperature set point" (decrease the amount of cooling). If you're not sure how your request or statement is going to be taken by others, make sure it's unambiguous by stating the [undesirable] current condition and/or the desired results: "I'm cold, please turn down the A/C" or "Please turn down the A/C to raise the temperature" or even "Please turn up the temperature setting on the A/C".

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