Where would I get the vent system cleaned?

You might try lysol spray disinfectant first. Do not use bleach.... it will ruin metal components. With car ac on at full blast spray into the vents on outside of car under wipers. You might try it first with ac in recirculate mode. If that doesn't fix the problem do it in fresh air mode. Also your dealer may have a foam to use too.

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Maybe you just need to change the cabin filter. They get 'stuff' growing in them . . Is it a Honda? What year and model?

'Curly'

if it smells "syrupy", you have a coolant leak somewhere.

Sometimes the airconditioner evaporator drain hose becomes plugges and the moisture won't drain and mold builds up in the evaporator causeing it to stink, there is a product sold to kill the smell and mildew,you spray or squirt it into the vents and the cowl vent. most auto part stores sell it

Tom

SoCalMike wrote in news:et-dnSV5Ia8gApfZnZ2dnUVZ snipped-for-privacy@comcast.com:

It does have a sickly sweet smelling aspect to it, but it doesn't smell like coolant. Again, it's something in the area underneath the cowling.

If I pull the cowling off and hit recirc, it doesn't come thru the vents anymore. If the cowling is on and recirc is on, it still comes through.