That's actually how many think you can prevent it because it keeps air paths dry. Not 100% certain of that though. I always leave mine on auto (all seasons) and it does a good job for me whether cold or hot outside.
Originally Posted by The X Men
You must get that smelly duct work problem from leaving the AC on all the time.
2013 x35i (Space Gray, MSport, CW/CWII, DHP, Premium, Premium Sound, Technology, BMW-Apps)
Retired:'09 C300 4Matic, '09 GTI, '06 750i, '05 C55, '04 R32, '03 M5, '02 GTI, 01 M5, '00 M-Coupe, '00 540i/6, '99 M3 Coupe, '98 M3 Coupe, '96 328i, ..., '86 4000CS Quattro, ... too many to list