Imagine a student, sitting in class. He stayed up until 1 a.m. finishing a very confusing lab assignment he still doesn't understand and can't help but doze off while the teacher is talking. The teacher notices the droopy eyes mid-lecture and walks to the all-powerful device known as the air conditioner. With a flick of a hand, the air conditioner roars to life, blowing out so much cold air it slaps the poor student into full consciousness. The student can not help but wonder who invented such a powerful and machine and how so much cold air can be blown into such a large room.

The man behind the air conditioner is Willis H. Carrier, father of the modern air conditioner. His moment of discovery came while working for a publishing company in Brooklyn. His job was develop a machine to help control the heat and humidity, which was causing problems in printing correct colors. Carrier's solution to this problem was the air conditioner, which was able to control the humidity, as well as the temperature in the room. His invention introduced the use of air conditioners worldwide.

Basically, an air conditioner is like a refrigerator. It uses the evaporation of a refrigerant, such as Freon, into a gas. An air conditioner has two sets of coils, one for the hot Freon gas and the other for the cool Freon gas. Usually in a school's air conditioning system, the hot gas coils are outside in a condensing unit, while the cool gas coils are inside the building. A compressor compresses the cool gas into hot gas, which passes through the coils and cools into a liquid. This liquid runs through a valve (known as an expansion valve), which turns the liquid into cold gas. The cold gas passes through the second set of coils which allows the Freon gas to absorb the heat and cool the air inside the building.