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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.
How much greatly depends on: Is it REALLY R-12 freon, or R-134a (The newer, greener stuff) Further, it also depends WHY the refrigerant went away. The right procedure will: 1. diagnose the problem/introduce a dye to find the leak. (I had a failure that turned out to be a reasonably inexpensive safety switch)