Modern air conditioning major appliances began in 1902 right here in Brooklyn. At the Sackett-Wilhelms Lithographing & Publishing Company, the humidity of the warm summer air made it difficult to apply the layered inking techniques. Electrical engineer Willis Haviland Carrier treated the air by blowing it across chilled pipes, cutting the humidity with the intriguing side effect of lowering the temperature overall.
Today, air conditioners use refrigeration, taking advantage of the physical law that phase conversion, the process of a liquid converting into a gas, absorbs heat. By forcing chemical compounds known as refrigerants to evaporate and condense continuously in a closed system of coils called evaporator coils, then blowing the cool air outward with a fan, air conditioners are able to chill a space not unlike a refrigerator.
Of course, to keep the cycle repeating, air conditioners must convert the gas back to liquid by putting it under high pressure, which has the opposite effect: creating heat. Using a second set of coils called condenser coils as well as a second fan, this heat is expelled from the air conditioner, which is why one end of the air conditioner creates cold air while the other creates hot air.
During the process of phase conversion, the air conditioner also dehumidifies the air–its original purpose as designed by Carrier–releasing the moisture in the air which must then be collected in drains or pans, or simply dripped on your head while walking down the street.