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We say "turn the fan up" when we want to increase the speed of the fan. That means the room will be cooler.

We say "turn the fan down" when we want to decrease the speed of the fan. That means the room will be less cool.

In some hot countries, air conditioners are supposed to make room cooler.

In other countries, air conditioners can be set to make room cooler in summer. But in winter, they can be set to make room warmer.

Say, There is an air conditioner in a room and it is making the room cool.

Now, Can I say "turn the air conditioner up" when I want it to make the room cooler (ie lower the temperature of the room)?

Can I say "turn the air conditioner down" when I want it to make the room less cool (ie increase the temperature of the room a bit)?

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    Turn the A/C up. Turn the A/C down. Air conditioners are for cooling, not heating. Some systems have both, so they are HVAC systems=Heating, ventilating and air conditioning.
    – Lambie
    Feb 23 at 17:31
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    Incidentally, the idea that hot is “up” and cold is “down” is not universal. A scale wherein the boiling point of water at sea level is “0°” and the freezing point of water is “100°” was proposed in 1742 by the Swedish astronomer Anders Celsius. The following year, the physicist Jean-Pierre Christin reversed it, producing the scale known to history, unfairly, as the Celsius scale. Feb 23 at 20:06
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    Turning the fan up or down is a different operation from turning the temperature up or down. Often both can be adjusted independently. Indeed everything else being equal, running the fan slower will produce a cooler output, as the air will have more time on the cold coil; there will just be less of it.
    – abligh
    Feb 24 at 6:45
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    @Lambie it depends on the country. In Australia (NSW), the thing that is called an A/C can heat in winter and cool in summer. Heating is just done by reversing the direction of the unit, hence the name reverse-cycle air conditioner, but colloquially it's just an A/C. For me, turning up the A/C means to turn up the fan speed of the A/C, but it leads to confusion. Feb 24 at 13:31
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    Does this answer your question? Use of the word 'lower'
    – Mari-Lou A
    Feb 24 at 14:54

6 Answers 6

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I would argue that the usage is unclear, and is best avoided.

I have a pet peeve with my refrigerator because of this ambiguity. On many refrigerators, you can control the temperature, perhaps with a dial that tells actual numbers, or says something like "min" and "max." Mine just has a screen with a stack of bars and you can press buttons to show more bars or fewer. But does more bars mean a higher (warmer) temperature, or does it mean more cooling power? I'm not sure! I've looked it up in the manual more than once and forgotten more than once.

I would say that in general and on average, "Turn the air conditioner up" would be understood as "make it work harder, increasing the cooling." However, there would still be enough confusion that one might ask "Wait—up as in warmer, or colder?" And enough that it would be a good idea to change the wording to something unambiguous: "Turn the temperature [or "the thermostat"] up." I think this uncertainty comes from the fact that we mechanism we use to control the air conditioning makes specific reference to a numeric measurement. That is, we adjust the degree number on the thermostat. To make it colder, we lower this number. This is the source of the confusion, and it's better to speak about the actual control.

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    Refrigerator UX designers have been making bad decisions for decades. I still remember the fridge/freezer combo I had where there were 2 dials, one which changes the overall temperature of both fridge and freezer, and one which changes the ratio between them. So let's say your fridge is fine and the freezer is too warm - figuring out how to make the freezer colder without changing the fridge temp as well was nearly impossible. Feb 24 at 15:20
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    @DarrelHoffman there's a point in every technology's development where controls and automation reach a peak of badness. In many things we're past that point, but domestic appliances seem to use some very dated ideas in many models. They probably sold a digital" model with the same compressor, fans, and airflow valves, but slightly more expensive electronics - for a much higher price
    – Chris H
    Feb 24 at 16:56
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    Don't forget the corollary "turn the AC down!" Do you want less air conditioning leading to a warmer environment or do you want it set to a colder temperature? Both usages of "up" and "down", in relation to AC are confusing and will, inevitably lead to further conversation to clarify meaning. It does not seem to be nearly as confusing when talking about heating, though.
    – FreeMan
    Feb 25 at 16:32
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    @DarrelHoffman that probably wasn't the fault of the UX designers. Fridge-freezer combinations typically work by actively cooling only the freezer department, and bleeding (as it were) some of the cold into the fridge. Regulating the temperature of both separately would require much more sophisticated control than only adjusting the “ratio” with some simple mechanical control of how much thermal flow to allow between the departments. The UX designers may very well have pointed out that this is awkward for the user, but they would have been vetoed by management because of cost consideration. Feb 26 at 13:45
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This usage is unfortunately both completely natural/idiomatic, as well as ambiguous and confusing. A native speaker might very well say "please turn up the A/C" and mean either "raise the temperature setting on the A/C, so that it becomes less cool" or they might mean "make the A/C more powerful, so that it becomes cooler". A listener might understand either of these meanings as the correct one, or might be confused and ask for clarification as to which meaning is meant. In my own family, we've had this exact confusion on multiple occasions.

That said, the intended meaning is usually clear from context, and understanding what the speaker actually wants to say. Other words around the statement will be able to clarify what it means.

I'm hot, could you turn up the A/C please?
It's too cold in here, could you turn up the A/C please?

Note that in American English (AmE), A/C never refers to heat, even if the same device provides both heating and cooling. A/C only refers to the device that cools the air. You could say "thermostat" to refer to both, or else use "A/C" for cooling and "heater" for heat. On a technical level, we use "central air" or "central heating and cooling" to refer to the system that does both.

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    Ironically, in AmE we often distinguish between A/C and "heat" even when it is one device (heat pump) doing both! Again, probably because our language revolves around the method of control, the thermostat, which is usually only in one mode or the other. Feb 25 at 16:38
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Even if heat and A/C come from the same device, they are separate functions. Heat and A/C then refer to functions on the device, not the device itself.

To make the device put out more heat, you'd say "turn the heat up"

To make the device put out less heat, you'd say "turn the heat down"

To make the device put out more cool air, you'd say "turn the A/C up"

To make the device put out less cool air, you'd say "turn the A/C down"

If the device only has a temperature setting and doesn't have independent controls for the heating unit part of the device and the cooling unit part of the device, then what you are adjusting is the device's thermostat and that is what can be turned up or down.

This is a US centric view. Countries where single devices are more common may have different local idioms.

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  • I think you’re referring to heat pumps, but the same problem remains with those as with separate heating and cooling systems. The only solution is to turn the thermostat up or down.
    – StephenS
    Feb 24 at 15:18
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    Downvoted because, sorry, this is technically how it ought to be used but in common usage most people don't have a single thought in their head about if they're adjusting a thermostat or a direct control (direct controls do exist, for example in cars). Not to mention if you're in someone else's house/car/etc. you can't sit there saying "turn the AC up if it's a direct control but down if it is a thermostat, please". It's much better to accept that this is ambiguous in common usage, and simply avoid it altogether--"make it colder, please". Feb 24 at 17:48
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I suggest you speak about the thermostat instead of whatever equipment it controls. In this way you can unambiguously say, "Turn it up in here, I'm freezing"; or conversely, "Turn it down in here, it feels like a sauna."

BTW, a reversible "air conditioner" that can move heat either out of or into a place is called a heat pump. They are attractive in areas with mild winters, as they can be more efficient than a traditional furnace or boiler.

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The turning up or down process is in conjuction with the power needed to run the fan and not the temperature I believe.

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Turning up the AC refers to increasing the "set" temperature on the thermostat, turning down the AC refers to decreasing that "set" temperature. The "set" temperature refers to what the system will maintain the temperature at in the room, house, etc...

That being said "turning the ac up/down" is more of a slang term that everyone is familiar with. So is it "technically" correct? No, its not. Will everyone know what you're talking about when you say it? Yes, they most likely will.

If you're curious I would say the most technically correct way of saying it would be "I am going to decrease the set temperature on the thermostat". If it doesn't switch between heating and cooling on its own, then you could change it to "I am going to decrease the set temperature on the thermostat, which is set to cooling mode". But those are very verbose statements that no one is really going to say unless they have a need to be specific.

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  • Funnily enough, I interpret "turn up the AC" to mean the opposite of what you indicated. As do other answers. So I suggest to you that it's not obvious and you may not be understood, unless the room is clearly too hot or too cold.
    – piojo
    Feb 26 at 13:46

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