Blue Mountain Oasis has just completed our yearly work on the central AC. As it turns out we were 3 gallons low on freon! I also learned, in 2010, Freon units will no longer be sold!

"As a result of the Montreal Protocol, a conference that grew out of international concern over the ozone-depleting qualities of CFC chemicals, the EPA is mandating the gradual phaseout of Freon, or R22 refrigerant. The new, non-ozone-depleting replacement will be R4-10A. In fact, some manufacturers have switched to R4-10A in some models already. While this new refrigerant works just as well, it requires pressures up to 50% greater than Freon, so it can't be used in existing equipment. Interestingly, the higher operating pressure actually improves efficiency slightly. In any case, there's no practical way to convert existing equipment."

If you are upgrading your system, be sure to stay away from a freon system which will be phased out.