Beginning in the fall of 2009 R-22 (the primary freon now in use) equipment will be phased out. All new outdoor units will be freon R-410a.
R-22 is a mineral oil based refrigerant and R-410a is a polyester oil based refrigerant. The two are incompatible.
Right now there are procedures available for flushing the old mineral oil out of existing freon lines between indoor and outdoor units. As of now there are no procedures to adequately flush indoor coils of the old mineral oil, thus requiring that the indoor coil and outdoor unit both be changed in the event of an outdoor unit failure.
If an indoor coil fails and your outdoor unit is over ten years old then we strongly recommend replacing both because if you have an outdoor unit failure in the future it may require us to replace both indoor and outdoor at that time or repair the outdoor unit beyond it's useful life and at much more expense down the road.
R-22 refrigerant and replacements for it will be available until 2030 and beyond in limited production. ONLY the outdoor units (compressor/condenser/heat pump) in R-22 will not be available, indoor coils will still be available as they are somewhat universal in the freon they require.