One problem related to defogger has been reported for the 1998 Volkswagen Passat. The most recently reported issues are listed below.
The a/c ventilation system is defectively designed such that it promotes the growth of bacteria which causes an awful odor when turned on. I would guess that it aerosolizes the bacteri and or fungi and sprays them at high speed through the ventilating system outlets. I do not know but wonder what potential health risk this poses to children, pregnant women and immunosuppressed people or others with chronic respiratory illness such as asthma and copd. Finally, I wonder if there is a theoretical or real risk of legionnaire's disease since the same risk factors found in airconditioners at hotels and building may be replicated in this automotive format. I would like your feedback and assessment of risk.