3-Series (E46, E90)Chat relating to the BMW 3-Series from 1999 to Current. Models include: BMW 316i, BMW 318i, BMW 318Ci, BMW 320i, BMW 323i, BMW 325i, BMW 330i, BMW 328 Ci, BMW 328i, BMW 325i/xi, BMW 330Ci, BMW 320d, BMW 330d, BMW 335d.
Changing the microfilter will help, but that's not the cause of the smell (usually).
If you run your A/C and then just shut the car off when you arrive at your destination, there is residual humidity / condensation in your vents. This molds, and that's the smell. This is particularly prevalent in high-humidity enviroments.
There is one solution: about 5 minutes before you get to wherever you're going, just shut the a/c off, and leave the fan on. That should help dry out the condensation in your ductwork.
I wonder if maybe the final stage is getting really hot and melting plastic or something. id pull it out and inspect it. the microfilters probably wont make that type of smell but if theyve never been replaced its a good idea to just replace them anyway. you didnt say what model you have.. e39?
it doesnt exactly contact the air vent but its mounted to the heater box so the smell could definitely come out the vents. The final stage units definitely get pretty hot even under normal conditions so if there was a problem with it it could get really hot. I cant say thats the problem but its definitely worth taking a peek at. If you find it is the older non-improved version you may wanna replace it irregardless.
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