Brilliant Air con cleaner.

[T-Cut]

The primary source of aircon smells is the evaporator matrix. This part of the system is continuously wet/damp in any car that has aircon on all year round. The matrix eventually gets coated in a bacterial slime that smells like a sewer (it's basically the same thing). To get rid of the pong, you have to get rid of the slime and the best way to do that is to tackle the matrix as directly as possible using a detergent/bactericidal foam. The best route is up the condensate drains under the car. Good quality aerosol cleaners have a long injection pipe to get the foam directly into the evaporator housing. The foam loosens to slime which dribbles out of the drains. You don't need to put foams into the vents or ducts because that's not where the problem lies. Also, the recirculating air bomb type deodorants used in the cab are only a temporary solution and can't affect the slime.

TC