The hissing sound makes me wonder if your switch isn't some sort of manual air recirculation switch. Take out the glovebox, and see if the activation of said switch make the recirc flaps move. If they don't move, look and see what does.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D