The reason this problem occurs, and the reason that the "turn the AC off first" fix works, is this:

The warm air coming into the AC system can hold much more moisture than the cold air that is exiting the system. Warm air can always hold more moisture than cold air - this is why cold fronts coming through can spark rain, why you see fog when you breath out on a cold day, etc. So, the "extra" moisture that the cold air can no longer hold condenses in the AC system, usually right on the evaporator coil or nearby. There is a drain at the bottom of the evaporator that allows most (not all) of this moisture to drain out under the car.

So, when you stop and just shut the car off, all of this moisture is still sitting on and around the evaporator still. Some of it drains, but some remains. This provides a lovely place for molds to grow.

However, if you leave the fan on for a few minutes after shutting off the AC, the condensate has time to dry - it's essentially blown back into the air in the car. The dryer evaporator housing and ductwork won't support mold as easily, and voila! No nasty smell.

The evaporator coil has lots of little fins and so forth on it to encourage heat transfer (just like your radiator), which is why it can be so tough to cure the problem once it's started. Spraying Lysol or something into the ducts doesn't necessarily get it into all of the nooks and crannies.

Matt

 

I work for a dealer and have also heard to not always use the recirculate, turn it off and let in fresh air every once in awhile!

 

[QUOTE]Originally posted by autopia
You might want to try one of these products:

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I like the 1Z product best.