Ever since I got my car I have noticed a noise coming from under the dash, usually when I turn the car off or I first start the car. Something runs for about 4 seconds and stop then start back up for 4 seconds. It was fine until recently, now it sounds like something is worn out and now it does the same thing but sounds like grinding. It isn't loud, but you can definitely hear it.

Any ideas what it is? I was thinking it might be an extra evap fan, but I can't find one in the diagrams. Could it be the coolant recirculating pump?

http://daytonamercedesparts.com/part...6&section=HVAC

seems like the passenger side.

So you have ruled out the main HVAC fan? It also comes on when the car is shut down to remove moisture from the system and is sometimes referred to as an "evaporator fan". There is no such animal as you have said.

AC motor needs replacement, i had something like that the start of the year. Something was def worked out, got it checked and they replaced the motor, I'm glad that i have extended warranty and don't need to pay for it, it was an expensive fix. I think it cost around 1500$ ++.

Hopefully that is not the case on yours....

The regular blower works fine for heat and ac.

I get plenty of air and only normal noises from that.

The sound it reminds me of is a small computer fan that has gone bad.

Do you have the dynamic seats with heat/cool feature? Those 6 fans in the seat bottom and back are of the computer fan variety.

I do not have the fans in the seat model.

I think there is a small fan on the comand system. I've heard something like that when using comand with car off in the garage. It was very quiet and I recall the sound of a small fan, but I don't notice when the engine is running at all.

I would start ruling out components by turning them on and off. First turn off climate and then drive some to see if sound is there. Then with car off in a quiet place, turn on comand using on button on front (not start button) and see if you hear the same sound.

its the ac fan, I took the housing apart and put a small amount of lithium grease on the shaft and it runs fine now.. cheap fix

papromike, how hard is it to get the motor?

I finally figured out exactly where the noise is coming from, the dome light assembly.
It must have a fan motor or something inside. I am 100% sure the dome light area is where the noise is coming from.

Anyone have any ideas? I suppose step 1 is to take it out and look.

Yes, there's a fan in there that people have posted about. I forgot what it's supposed to do exactly.... something about air circulation for a temp sensor? There's a reason it stays on after the engine is shut off.