[wwest]

De-misting MUST involve lowering the relative humidity of the cabin atmosphere, specifically that at the surface of the windshield or flowing across same.

In most cases that involves HEATING the cabin atmosphere to lower the Rh, relative humidity, and/or lowering the windows slightly in order to more quickly PURGE the high humidity cabin atmosphere.

FORCED fresh inlet airflow AND OUTLET AIRFLOW will abate the rise in cabin Rh due to human metabolism thereby significantly lowering the onset of interior windshield surface fogging.

But once condensation has formed, or begins to form.......HEAT!

And let's not have some I@#%$ suggest using the A/C, the A/C in our 911's is ALWAYS in recirculate mode, plus, BIG PLUS, mother nature may not be in the mood to be co-operative.

Oh, the only time I have even been tempted to use the fresh air blower in my 78 Targa is with top on as a shade from a hot Kansas sun at mid-day. Don't think that I have ever considered using it at all in climatic conditions conducive to windshield fogging.