Florida can claim the first attempt at building an air conditioner, when Dr. John Gorrie (1803 - 1855), an American physician, created an ice-making machine in Apalachicola to help patients suffering from malaria and yellow fever. Dr. Gorrie's machine blew air over a bucket of ice for cooling patients' hospital rooms.
However, in 1906, the modern air conditioner began to take shape when Willis Carrier patented an 'Apparatus for Treating Air' (U.S. Pat# 808897). He began installing the machines in factories, and in 1928 developed the first residential 'Weathermaker,' an air conditioner for private home use.
The rest is history.
Today, most homes have air conditioning, and cooling and heating accounts for at least half of your utility bill, so maintaining your a/c unit is vital to saving you money.
Here's a video on what you should do to get your air conditioner ready for summer: