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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 2000 Saturn refrigerant is not Freon R12 it contains R134a. Add it at the Low pressure port. You have a leak or it would not be necessary to add refrigerant. It is illegal to add refrigerant to a system with a leak without first repairing the leak.