Refrigerators and freezers built before 1995 contain chlorofluorocarbon (CFC) refrigerants (commonly known as Freon). These substances contain ozone-depleting chemicals that destroy the ozone layer and are also powerful greenhouse gases. Improper disposal of CFCs can present a danger to the environment. Modern cooling units use ozone-friendly hydrofluorocarbon (HFC) refrigerants, but even these must be drained carefully, as they are considered greenhouse gases.
In most cases, the recycler or landfill handling your appliance disposal will drain the refrigerants themselves. But if you are responsible for draining your fridge or freezer prior to disposal, find a certified refrigerant reclaimer to do it.