Freon is recycled throughout an air conditioning unit, and should not need to be added to the unit unless the system has a leak. In some areas, Freon is a regulated substance and cannot be obtained without the proper licensing.
Freon is a heat transfer fluid refrigerant that collects heat from the air within a building, cools it down and then recirculates it throughout the area. In the areas where Freon is not regulated, it is possible to obtain Freon and add it to the air conditioning unit without professional assistance. Check local regulations prior to purchasing Freon, and consult a licensed professional if required.