ML430 ('99) AC drain

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Where is the condensation supposed to drain (from the car's air conditioning system)? Perhaps the drain is blocked. I'm not finding any water dripping and fear that it may sometimes collect and occassionally begin to stink. I've cleaned the in-cabin (underdash) filter element, and it did not smell. After use of the AC, if the vent-fan is left on, a sublte odor, like old leaves(?) becomes apparent.