Noticed on my 09 C300 what seems to be the blower fan running at very low speed when I listen at the PS side engine compartment near the firewall/battery box with the SmartKey inserted...if I remove the key the fan appears to stop only to restart if I insert the key.

Does this refer to some air purge I vaguely remember reading about and, if so, how long does the fan run ?

Thanks for any info...

That is where the blower fan for the climate control system is located. Although I'm not aware it running under such conditions.

I've never narrowed this down, but I can hear this with the car off in the garage, and while the car is locked. It sounds like a fan too. No idea what it is, but it's never been an issue so I just leave it be, I guess.

The dealership told me the climate control system monitors humidity, and that sometimes when it appears to be running it is actually just dehumidifying.
I don't totally believe this as the compressor would need to be running to effectively dehumidify. However, if you had been running A/C and the coils were still cold it could be somewhat true.

I don't buy the dealership on this one too. Yes, the compressor, and thus, the engine, would have to be running for this to be true.

Your dealership sounds like a clot!

It's a cooling fan for the electronics/computer etc. The fan starts when you open the door and turns off about 10 mins after you shut down & leave the car.

You can usually only hear it in a quiet enclosed space ie your garage

HTH

The argument is logical in my books. However, I sometimes do hear it after my car is in a hot garage after it has been off for a day, if not longer.

Don't know about the MB but my Volvo would do something similar. It was a fan that ran to dry the cabin air filter so it didn't get mold/mildew buildup.

HOLY MOLY. I would have never guessed that - and it makes perfect logical sense to me.

Thank you

It does make sense. But, so does the electronics fan theory.

Thanks for the feedback...notice i only hear the fan when the A/C had been running BTW. I like the keep cabin filter dry theory best.

I agree. And now that I think about it I only hear the sound after running the A/C.
Depending on fan placement this could also dry the coils and any residual moisture in the ducting.
I have read in other car's owners manuals in the past to turn off the A/C a few minutes before you plan on exiting the vehicle and to let the fan run for this exact reason.

Fan runs with warm air after start up and after AC has been used. Dries out the system so no mildew builds up and no AC smell like in cheaper cars.


My wife's Mini smells like a wet towel after she has used her AC. My C-class has zero AC odour and I have been using the AC constantly lately due to the high summer heat we have been having. Her car is 2 years old and stinks while mine is almost 9 so Mercedes for the win on that one.

I've never noticed that but I do hear what I think is the Comand's fan running.

It is def the blower door opening. Take off your battery cover and you will see a plastic cover where the firewall should be- when you put the key in, that cover lifts up like a garage door and you can see the blower.

I too believe this is the reason for the sound. My cabin air filter smells like updog...so the noise believed to be related to AC/humidity removal, does not work in my car.

i need to get around and change that cabin air filter (my car has 37k miles on it).