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This means that breathing low concentrations of freon from a leaking refrigerator or air conditioner over a long period of time is unlikely to have a cumulative effect, and thus few, if any, long term health effects.
The big issue today in using Freon and other refrigerants is the elimination of CFC's which are chlorofluorocarbon refrigerants. These new refrigerants are required to have low ozone depletion potential and low global warming potential, as well as keeping energy efficiency in perspective.