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For that matter, air conditioning could include humidifying or dehumidifying, but it doesn't: only cooling. Why weren't air conditioners called air coolers?

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You can use an air conditioner as a heater - just face it the other way – yoozer8 Oct 6 '11 at 0:09
@Jim or you can face the refridgerater the other way – Phonics The Hedgehog Oct 6 '11 at 0:10
Seriously, though, I had a similar understanding of the expression 'air conditioning' to mean cooling, as opposed to heating, whilst living in Victoria, Australia. It was not until I moved to NSW that I heard the expression being used for both. I suppose the meaning differs depending on where you live.... – Bill Oct 6 '11 at 0:29
I suspect that in most people's minds the term "air conditioning" is synonymous with cooling. Particularly in warmer climates, the most common requirement is to cool an indoor space. Of course, making a room comfortable may at other times of the year require raising the temperature. A more inclusive term such as HVAC (heating, ventilation, air conditioning) is useful, but hasn't caught on here in Australia. – Snubian Oct 6 '11 at 0:59
Yes, and why do we call those things "elevators" (or "lifts" for you Brits) when they spend 50% of the time going down, not up? – mickeyf Oct 6 '11 at 14:13
up vote 5 down vote accepted

According to the Oxford English Dictionary, air conditioning has changed in meaning over time:

Originally: the process of cleaning air and controlling its temperature and humidity in connection with certain manufacturing processes.

Now usually: the process of controlling the humidity, ventilation, and air temperature in a building, vehicle, etc., esp. to maintain a comfortably cool atmosphere in warm conditions; (also) an installation or appliance which performs this process, an air conditioner.

The term was first used in the original sense in the early 1900s:

1909 S. W. Cramer Useful Information Cotton Manufacturers (ed. 2) IV. v. 1395, I finally hit upon the compound word, ‘Air Conditioning’‥. Suggested by the use of the term ‘Conditioning’ in the treatment of yarn and cloth.

1930 Engineering 11 July 34/2 Air-conditioning is dealt with fully, with the methods for washing, cleaning, humidifying, cooling and drying the air.

By the later part of the century, it was used solely to refer to cooling warmer air:

1987 C. Phillips European Tribe i. 11 Only the odd car rubbering by in the boulevard below and the hum of the air-conditioning disturbed my sleep.

So air conditioning was originally the cleansing of air, which already included temperature control. However, the meaning shifted over time to refer to any temperature control--but usually the cooling of warm air. It also shifted from industrial to more personal scope.

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Probably the reason that air conditioning refers to "cooling" is because central heating was introduced first. Then the remaining problem to be solved became one of "too hot," rather than "too cold."

Also, air conditioners (and refrigerators) use a coolant called freon, that "conditions" the air. There are no similar chemicals that act on the air when it is heated.

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I suspect that at the time they were introduced "conditioning" sounded like a comforting and effective thing to do - rather than merely cooling. In the same way that food mixers were called "food processors" when they were introduced because it sounded modern and technical.

A close ancestor to the modern air conditioner units was first made in 1902 by an American engineer by the name of Willis Carrier. The machine at that time was called "Apparatus for Treating Air".

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