Smell When Turning on Air

[WangTa]

Ok guys...this is a random post, but I need help because I'm absolutely BAFFLED.

My M has 9,000 miles on it. Looks pretty darn new. However, whenever I turn on the air vents, the smell coming from the vents smells really really strange. Like old pee, animal-nest like. Is it possible a mouse nest is behind the vents? When running AC through front vents, it smells ok...but when I turn on the front defroster - man, it straight up stinks. I have no idea WTH it is.

I've cleaned the inside of the car thoroughly - vacuumed, applied Zano cleaner and leather conditioner (Smelled good until I ran the AC!).

I have no idea what to do or even how to check this. Have any of you guys had this problem? Again, the car looks new inside and out...

[ajvee]

I've heard of this exact issue and there was some speculation that the cabin air filter was the cause and needed to be replaced. I would probably check into this first.

[Youngbp04]

My 335 does the exact same thing! I have 14k miles on it. Smells ok with AC and terrible with heat, it is bad enough where even my GF is complaining about it.

Dealer told me when I first picked up my car that it was the rust protectant and sealant burning off. But still smells funky!

[WangTa]

Originally Posted by ajvee

I've heard of this exact issue and there was some speculation that the cabin air filter was the cause and needed to be replaced. I would probably check into this first.

Really. Where is this cabin air filter? I don't have the manual on me right now. Is this covered by warranty (half joking)

[WangTa]

Originally Posted by Youngbp04

My 335 does the exact same thing! I have 14k miles on it. Smells ok with AC and terrible with heat, it is bad enough where even my GF is complaining about it.

Yes - exactly. I was actually semi-ok with it, but my gf noticed and was like "what the fuuunk is that?"

[WangTa]

Originally Posted by ajvee

I've heard of this exact issue and there was some speculation that the cabin air filter was the cause and needed to be replaced. I would probably check into this first.

Hmmm, you may be right. I just found this video - check at 2:13, that looks like crap where mold, nastiness could live...

[quiksi]

one way to avoid that is before you turn the car off after running a/c, turn the a/c off and crank the fan up for a while to help blow out any moisture that might have accumulated in the system

[JIO]

The M3 has two cabin filters under the hood...one on each side. You have to remove a few screws like in the video. The charcoal filters are not cheap to replace but under scheduled maintenance, they are replaced free.

Usually the smell comes not the filters but from inside the A/C unit under the dash. The moisture formed causes bacteria and mold to form which causes the smell. About the only way to rid of the smell is shut off your A/C a few miles from home so the moisture is evaporated. Of course, if it's 100° outside, you don't want to turn off the A/C so soon.

[Mineral M3]

.

[Mineral M3]

It's bacteria in the pipes. If you go to a dealer they should be able to clean your system if not you need to find an air con company. They normally spray a chemical into it. It happens because you probably haven't used the air con enough and it's got damp. The air con will dry out the system so try and use it in the winter too. Hope this helps.

Ps you could leave the air con running for about 30 mins on medium temp and all the windows open this should dry it out. I did this when I worked in the motor trade.

[Sean@PYSpeed.com]

I used to get this too. But my 15k mile oil change took care of everything!

[DBH]

It's bacteria build up in the ducts. This is not uncommon in most newer cars (not just BMW's). Take the car to a dealer or auto a/c place. They will spray chemicals into the ducts that will kill the bacteria and eliminate the smell. However, to keep it smelling nice your will need to turn the a/c off a few minutes before arriving at your destination to dry out the moisture from the ducts.

[piloto]

Try this stuff. You spray it down the vent and it helps kill the bacteria.

[WangTa]

Originally Posted by DBH

It's bacteria build up in the ducts. This is not uncommon in most newer cars (not just BMW's). Take the car to a dealer or auto a/c place. They will spray chemicals into the ducts that will kill the bacteria and eliminate the smell. However, to keep it smelling nice your will need to turn the a/c off a few minutes before arriving at your destination to dry out the moisture from the ducts.

If I bring it to a BMW dealer, will they have the spray stuff and do this for me?

[cwidjojo]

This happened to me when I left the car for a month. When I came back, the heater started to smell like horse sh!t (not a hyperbole). Now its fine again.

[Ctm309]

Originally Posted by piloto

Try this stuff. You spray it down the vent and it helps kill the bacteria.

What the dealer uses and charges big $$ for "system clean out"

I have used it and it really works: www.detailersdomain.com

[kouhii]

If you have an 09, press the REST button right after you turn off your car after running the AC. This will keep the fans running for around 15 mins and will continue to run even if you get out of your car and lock it.

[JCtx]

Originally Posted by JIO

The M3 has two cabin filters under the hood.

There're FOUR , 2 on each side.

On the stink, it's the evaporator unit. My cabin filters look like new, and everything below the filters is clean (just did a brake fluid bleed, so I know ).
As noted, A/C compressor needs to be shut off before you arrive at your destination. This car is THE WORST I've ever owned, so something in the HVAC design is f***ed up. My car has 7K miles, I live in the freaking desert, and still smells a little funky even after always shutting off the compressor before turning system off. At least it's tolerable. Another 'nature of the beast', I guess .

[conradb]

My 2007 335i used to do that. It's just the smell of plastics and the humidity left over in the vents. There's no way to fix that unless you blast the entire system with air freshener frequently haha

[WangTa]

Originally Posted by conradb

My 2007 335i used to do that. It's just the smell of plastics and the humidity left over in the vents. There's no way to fix that unless you blast the entire system with air freshener frequently haha

No dood, this does NOT smell like plastics, etc. Smells like FUNK. FUUUUNK.

[BruinE90]

Originally Posted by kouhii

If you have an 09, press the REST button right after you turn off your car after running the AC. This will keep the fans running for around 15 mins and will continue to run even if you get out of your car and lock it.

where is the REST button?

[radiantm3]

Am I the only one who never turns off the A/C button when the air vents are on? I don't have any smells ever. During decent/nice weather my windows are down and vents are off, but I never turn off the a/c button.