Hello! I love this Mercedes Forum! We have fixed a number of problems on our 96 S420 with your help! 2 days ago, we got into our S420 and a whirring fan noise began next to the sunroof controls in the interior lighting cluster. It begins when the engine is turned on and thankfully ends once the engine is turned off. Even our great local mechanic (35 years of MB experience) is not sure...possibly something to do with the interior temperature control...it is so annoying...any advice?? Thx!

 

There is a fan called the "aspirator" in the light assembly that sends air temp samples to the heater

 

Thank you, Peter! Any advice as to how to stop it? We have done alot of the work already ourselves on our S420, but when it comes to the electrical portion, such as the aspirator, we want to make sure that we disturb nothing else, since the car is performing flawlessly other than the aspirator noise.
Jay

 

Try this link,
http://www.mercedesshop.com/Wikka/W140AspiratorMotor

 

Consider also that something could have got lodged inside the aspirator compartment and the tiny blower motor/aspirator fan. Such as a piece of cloth or dirt particle etc. I had your symptoms once and was able to lightly blow air into the slotted vent to the small aspirator motor (I used a keyboard cleaner,with extra care not to applytoo much air pressure, cleared out the small blockage I had). Worst case the tiny fan or tiny fan blade(s) are damaged and the aspirator motor has to be replaced. As I know it, theoverhead light assembly has to be removed to access the mounting of the asiprator assembly, not just pop-out thesmall the aspirator vent grille. Part is not expensive, $77.00 at www.autohausaz.com. Item is called: AC/Heat Sensor; Miniature Blower; For Cabin Air Temp Sensor. part number for my car is: 1408300008.


Testing and Inspection







In - Car Temperature Sensor (B10/4), with Aspirator Blower











Check in - car temperature sensor aspirator blower by placing a small piece of paper (approx. 1/2" sq. ) over aspirator blower vent grille with ignition "ON" . If there is sufficient ventilation the paper will remain on the vent grille, if not check aspirator blower for voltage supply and function. The after - run time for the blower motor is approx. 1 minute.

 

Many thanks to Peter and Bill for their advice and help. We look forward to hopefully conquering our noise problem within the next few days. We'll let you know of the results! Great to have friends in the Mercedes world! Thank you!

Jay Rice

 

Good job, guys! I'm proud of you all.