BLUECUBE

Hello Everyone!
Decided I should finally make a post on this problem as it's been haunting me since I got this car 2 years ago.

My 2005 S-430 has a problem with the blower motor changing fan speed when I turn the steering wheel. You can actually see on the climate control unit the fan speed changing as I turn the wheel.
This is somewhat of a difficult problem to describe over text so I have attached a video of the problem to better detail it.
A few days ago I learned of a "fan speed controller" that is hooked up to the blower motor and located in the passenger foot well and that sounds like it could be the problem but before I go tearing my interior apart, does anyone have any other ideas or has anyone else experienced a problem like this?

Things I have tried so far:
-Replacing the climate control unit
-Replacing the car battery with a new one
-Resetting the climate control unit and clearing any errors (There are no new errors)

Thanks!

tim687

That is stock on all Mercedeses, as soon as you really start to drive it, it will blow more air into your face to help you cool down from the intensive driving.

Nah all the jokes aside, I'd look into a canbus related issue. There might be two wires that are not attached properly and cause interference that gets picked up by the AC controller as fan speed changes.

Does one direction increase the fan speed and the other decrease the fan speed?

BLUECUBE

When I first got the car I almost thought it was a kind of weird safety feature XD. I only realized how annoying it was when you're trying to drive in a parking lot with the fan on high.

But in all seriousness, it does not increase/decrease based on how you turn the wheel. Basically, if you set the fan speed to anywhere above 3 "bars" (Bars being those little indicators on the climate control screen) at certain points when you turn the wheel the "bars" will always drop back down to 3. It doesn't stay that way it's almost like a dead spot or something, or the wheel is shorting out something when you turn it in certain positions. I posted this same problem on a Facebook page for W220 and a guy over there said it could possibly be a bad "steering position sensor". Sounds plausible but after some research, it sounds like I would have ESP warning lights if my steering position sensor was bad. I think I may just try and replace the blower motor and fan controller as they are cheap and I need to rule them out.

tim687

I'm not sure if those will fix it, as the change of fan speed is reflected onto the display. I assume that the motor and the controller do not have a feedback signal back into the AC panel

BLUECUBE

That actually makes me think about something. My dad has a Benz, an 08 GL450, and he had problems with his AC acting weird (Not this way specifically but close enough) He fixed his by cutting a wire going to the climate control module and soldering a diode onto it. It's a proven method. Supposedly it blocks some kind of signal going back into the control module and screwing stuff up. I wonder if that could fix it? I just don't know which wire to solder the diode on to.

tim687

You could give it a try. Search for the AC controllers system function document, there should be a pinout available on there

Bugsi

This might sound crazy, but I was pretty sure the S500 has a feature that detects when you're in direct sunlight or not, and boosts or cuts the fan speed in response. You can push the button/knobs to put the system into manual mode and see if the problem goes away.

tim687

There is an sun sensor on the hood. It's the little dpme in the middle of the hood near the windshield. You could try to cover that up, or disconnect it to check if it's shorted out or something