Refrigeration units, commonly known as air conditioners, are mechanical systems that remove heat and moisture from the air by passing it over a cold surface. When warm, moist "inside" air is blown across the surface of the unit's cooling coil, the air temperature drops and the water vapor in it condenses making the air cooler and drier and therefore more "comfortable".
When the "outside" air is above 75°F, mechanical refrigeration is usually required to lower the inside temperature and humidity to make people feel "comfortable". Refrigerating air for comfort inside the home, (called air conditioning) is far more complicated than heating. Instead of using energy to create heat, air conditioners use energy to remove heat. The most common air conditioning systems use what is known as a vapor-compression cycle similar to the one used by a refrigerator.
The primary difference is a refrigerator moves heat out of its interior and releases it to the surroundings, (usually the kitchen), while air conditioners take heat from inside the house and release it to the outside environment.
Home air conditioners have compressors outside which contain a fluid refrigerant. This refrigerant can change back and forth between liquid and gas states at temperatures in the 40°F to 50°F range. Just like water when it boils, as the refrigerant changes from a liquid to a gas, it absorbs heat, and when it changes back from a gas to a liquid, it releases heat. By changing state, refrigerants move heat from one place to another.