If the viscous fan clutch is good, and the low speed fan does NOT come on, I would suspect that one of the wires to the resistor has burned off. (naturally, I would check any fuses first, and then verify that the fan works to begin with).
There are probably other things to check - but - I mention the resistor, because it has happened to me 3 or 4 times in the last 5 years, and I'm not the only one it has happened too.

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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