Originally Posted by JHZR2
That makes zero sense. Do you understand how an automotive AC system works?
What exactly is your "organic"? R134a? Yeah right. An evaporator or any joint could seep refrigerant, and it can have an odor at high concentrations, but if they were sniffing refrigerant, for one thing it wouldnt last long since it would be all gone quick, but if it were in a concentration to smell it, it would. One out faster and be more noticeable with the AC on since the system runs at a higher pressure than if it were off and just equilibrated thermally with the ambient.
Organic from some bacteria or mildew I will agree with. I get this sometimes in my 135i and my Saab. The basis of the evaporator closing with the HVAC system turning off is plausible for stink after the HVAC is turned back on (orpine when the car is turned off then started back up). But the situation here occurs when the AC only is turned off (air still flowing), which means it is going through the evaporator and ducting, just in a monster state, which for whatever reason creates the smell.
Well, I'm just describing what happened to my car, organic or not, the smell was there, with AC or just fan... And after replacing the evaporator, the smell is gone. Coincidence ? Who knows.