Pontiac Vibe, A/C

My 2007 Vibe has a constant mildew smell in the AC and heat ventilation system. I have taken it to the dealer numerous times and they have cleared the drain, flushed the system out numerous times and replaced the filter twice. However, shortly after they work on it, within a day or so, the smell returns. There are no dealer recalls regarding this issue. Please advice

Water condenses on the AC evaporator as the AC is being used. Obviously not all of it drains out onto the road, and the water that remains in the system after you turn it off is allowing mold to grow.

Some suggest leaving the AC controls ON even when the engine is shut off as a way to promote a little more airflow through the system. I don’t know if it works or not, but it’s worth a try.