Refrigerant leaks: Lots of older air conditioning system still use Freon as the refrigerant. This is completely safe, that is till the a/c system establishes a leakage. Freon is a chlorofluorocarbon and will damage the ozone layer if not handled correctly. Regular air conditioning unit upkeep can show up minor leakages before they become major issues-- both for the efficiency of your A/C and the s