My C240 is much like my asshole. When everything is working it's great....however when its not i feel shity. There is a humming from the overhead light module control when the vehicle is turned off. The controls all work properly ie: the dome lights front and rear and the power sliding roof. This car does not have the tele=aid feature on the module. What could cause the humming and how do you repair it? It is draining the battery when the car is turned off. When I remove the number 9 fuse the noise stops.
We have been discussing same thing in "BATTERY DRAIN" section
I know what is it. I have same humming. Some people have also.
It is a fan of temperature sensor. It sucks cabin air to measure it's temperature. This sensor is a part of air-conditioning system.
I am also worried with it. I was sitting 15 minutes in the car and fan did not stop. I cannot recall if this humming was ALWAYS present or emerged after I disconnected negatibe cord of the battery. Maybe air-conditioning brains became damaged or something....need to hear from the experts.
I am seeking help aslo on this matter 'cos this humming is really annoying I agree.
Turns out that this overhead temperature sensor N70/b1 was only available in c class autos built before 31-05-02. It works inconjuction with thetemperature sensor inthe climate control unit. MB mechanic initiallized my climate control today and the overhead sensor went off after a short time. This is normal as it does not shut off with the ignition. Got home and the overhead sensor would not shut off again. Thinking of disconnecting the overhead sensor as it is draining my battery over several days of not running.
I had the same issue on my e 320, drove me nuts!!! I replaced the fan and all was good. I'm no mechanic and it seriously took 10 minutes. I used one of those small screw drivers for glasses.
I was just in there looking to hard wire my radar detector. I was measuring the voltage of the different wires looking for a switched wire. I kept feeling this breeze and couldn't figure it out until I put my ear to the assembly. It is a fan running just as you discribed here. Is it supposed to shut off when the car is off? Should it run for a few minures or what? I don't drive the car often and keep a battery tender on it so I have never had a problem yet. I am interested in additional comments.
I have finally soved my problem with my over head panel and my blower motor. After going to the dealership ($200) they replaced the unit ($822 Canadian available in the US for $500.00) and the motor shut off in about 12 seconds after the ignition was shut off and, this is very important, THE VEHICLE IS LOCKED!!! If the vehicle is not locked the blower motor does not shut off. You can put a small piece of newspaper over the motor and it will stay (this is the recommended method by MB) to test it. If the blower shuts off the paper will fall. The blower motor is actually sucking air in to sample the temperature and then signals the climate control unit to heat or air condition.
Last edited by menno01 : 08-11-2008 at 07:30 PM.
Reason: spelling
Thank you for posting your findings. I put a small piece of toilet paper on the overhead fan vent and it stuck there long after I closed the car door. The dealer told me that these things can run for 20 minutes so not to worry. Well it was over an hour and the paper was still stuck to the vent. As soon as I locked the doors the paper fell off in about a minute. I feel much better now that I don't have to worry about draining the battery.
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