I used to smell bad air from the acu. Mine happened only on the initial blast of fan air when I turn on the acu in the morning. The sour smell will quickly disappear once the compressor was turned on. One of the supervisors of the car dealer advised me to remove my acu air cleaner and keep the thermostat to full maximum position. It didn't work.
I also fumigated the interior with anti-mold and mildew product made in Japan. It didn't work.
I sprayed Lysol (two types of scents) into the air vents. Didn't work. I tried to mask the smell by pressurized air freshener and hanged that little thing in the air vents. Didn't work.
I came to the conclusions that any chemical preparation inside the car has a bad effect on the acu air. The other conclusion is that the air inside the car gets polluted over time and you need to replace it with fresh air. Of course, if your car's interior is dirty, so will the circulating air be.
Finally, I removed all air fresheners from the car. Totally. No more spraying of anything, no more California scents. I vacuum the car's interior at least once every week. I remove and clean all floor mats and hang them under the sun and opened all doors and expose the car's interior to direct sunlight for several hours every Saturday. Before I turn off the engine at night I leave the fan turned on for about 3 minutes with thermostat turned to heater (mild) to blow dry the acu air ducts. I wash the seat covers once in two months. I do not allow eating inside the car (mostly ignored by my wife and daughter.)
Quite a lot of work on my part, but it worked. The bad smell of fan air was gone. Wala na yung maasim na amoy. Now that the air inside is as fresh as outside I get a hint of that showroom smell you were talking about, hehehe.
I also have an air ionizer on the cigarrette lighter and I am aware that some cars have no air cleaner on their air con system. Mine has and I have just replaced it with a new one. But even discounting these two items, the above practice worked very well in keeping my car's interior smelling clean and natural. Most of all, we are no longer bothered by the smell of car fresheners! Alam nyo, sa totoo lang, napakaginhawa ng pakiramdam namin nung mawala na ang air fresherner sa loob ng kotse namin. Sa amin lang naman po.
Hope this helps.
