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Discussion Starter #1
Hi guys,

I've got a merc C200 1996 with AC but not electric climate control just the fan speed knob.

When I turn the fan on it only sometime comes on and not at the right speed. I might have it on speed 1 but it blows at speed 3. Turn things off and on again and it might work at the right speed for a little while. The obvious fault is the variable fan switch. My question is can these switches be rebuilt? Is there a reasonable priced replacement switch I can use? Or is there another way to fix this problem.

All hep is appreciated.

Cheers

Aussie2802
 

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1995 C280 (165K mi)
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1,545 Posts
You know, I am having similar issues. My climate control is electronic.

The system always comes on at ignition to a setting of 74 degs, lowest blower setting and blowing at the foot well. The system, resets to the above parameters even when I change the settings and then turn the car off. It never used to be like that.

Also, while driving the temp designation changes from F to C and the blower motor speeds up and slows down randomly.

Can I reset the system?
 

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Discussion Starter #3
Hi MB W202,

Unfortunately yours sounds like a cpu / logic issue. Im not sure if you can reset the climate control. My issue is different as there is no CPU that controls my fan...mine will be a mechanical switch issue, I think.

Can someone correct me if I'm wrong.

Cheers

Aussie280
 

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Mercedes w202 C180 1996 | M111.920
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58 Posts
I think you're right aussie2802 and I think maybe I have the same problem. The fan change speed by itself, I usually have it on 2, but it seems to jump to max (5) now and then, if I just push on the level switch it jumps back. So probably something mechanical, regulator or something. I'll let you know if I'm able to fix it.
 

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1995 C280 (165K mi)
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That sucks. I have heard that there is a way to diagnose my system I just don't think there is a way to reset it though.
 

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'97 C200 Blue
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78 Posts
I've got a '97 C200 with the manual fan switch and I also have the same thing happening.I turn on the A/C to 3 and the fan seems to go full speed for a while then settles down to the 3 setting, I thought that it was something to do with getting the temp down quickly before resuming normal operation. I also seem to have a relay that makes continuous clicking sounds for no reason when I turn off the fan, sometimes it starts clicking even with out the fan turned on, any idea's, perhaps dirty contacts? The noise is coming from the left hand side of the dash.
 

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99 C230K
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109 Posts
I have the fan that likes to change speed by itself as well. My car has the knobs.
Also, when I turn the fan off, I get this sputtering noise that's most prominent in the passenger side front foot well. There's a black vent that comes out from the center on the inside of the foot well, and the sputtering is loudest when observed from that vent (as opposed to the vent in the drivers side foot well).
Sometimes, when I get annoyed of the speeds changing, I fudge around with the knob a bit, changing the speeds plus or minus 2 notches, then bring it back to my desired setting. That seems to settle the AC blower. From the looks of it, though, it seems like a mechanical issue more than anything.
 

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Discussion Starter #8
Seems to be common fault

Thanks guys for your responses...it seems there is a common fault with the manual fan switch.

Since this is the case Mercedes would have a standard fix,,,can someone comment?

Also someone must have tried and succeeded in fixing this problem in the past...please share your experience and fix for the rest of us.

Cheers

Aussie2802
 

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I sprayed mine with WD-40 or any electrical contact cleaner to fix the fan speed problem.

You can just pull out the knob, and spray generous amount of WD-40 or electrical contact cleaner to the center of the knob. That should fix the problem, at least on mine.

Please report back with your results, thanks.
 

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C220 1996, C300 2010, E240 2005
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56 Posts
I have the same problem.
I thought the clicking might be related to switching the fun on and off. What do you think?
To ensure the compressor is not getting on and off, etc. I press the ECO button during the winter (until I'll have a better solution).
At MB garage they quote about 2000$ for the unit. Of course I didn't took it.
 

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Mercedes w202 C180 1996 | M111.920
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I sprayed mine with WD-40 or any electrical contact cleaner to fix the fan speed problem.

You can just pull out the knob, and spray generous amount of WD-40 or electrical contact cleaner to the center of the knob. That should fix the problem, at least on mine.

Please report back with your results, thanks.
I don't think you should use WD-40 there. This isn't a electronic cleaner and will make a oily surface on the electronic parts, which may after some time make it worse. Buy something that's made for electronic cleaning (i.e not oil).
 

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1962 W111 220SE Coupe
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2,289 Posts
Mine does this too but it seems like no-one found any remedies yet? I have not seen the back of the HVAC panel (mine has the knobs) but can anyone confirm if the dials for selecting fan speed are separate units or part of a whole assembly that would need replaced?

Regarding the WD40/electrical cleaner suggestion, even electrical cleaner is not ideal as suggested because it should be allowed to completely dry before you fire up the electronics to avoid any potential for shorts, and it would be difficult to see if the area is dry just from spraying via the front. I wouldn't do it on my car.
 

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Mine does exactly the same thing but it's even worse.
I only noticed it after I had my car stopped for a few days and I tried to start the car and my battery was dead, I got a replacement and the next night I was washing it and I heared this noise from the passenger side engine compartment. I went inside and the blower motor was on with the car completely turned off.

I'm still looking for a way to fix the knob as it goes on and off and changes "position" by itself.
 

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C200 Classic 1997
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90 Posts
Mine (C200, 1997) also messed around. I sprayed with WD-40 and it was fine a month or so but now it seems to have packed up completely, so no aircon. The fan seems to run at its slowest speed when the car is going but no setting on the switch works.
 

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1996 C220 2007 ML320 CDI
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You could try cleaning the knob with electrical contact cleaner as stated above. Usually however, what controls blower speed is the blower motor resistor. The knob/climate control just supply a voltage to the resistor, and depending on the input voltage the resistor regulates the blower speed. If the speed is changing for no reason I'd first suspect the blower motor resistor.

For those with the electronic automatic climate control, when the unit decides it needs a change in blower speed when in the automatic mode, it should display the commanded change in speed in the fan speed selection. The module decides on the fan speed depending on how close the target temperature is to the current cabin temperature. The closer the temperature is, the lower the fan speed, with a minimum of notch 3 (for those with the display type CCU, the older automatic CCU has less fan speed notches). Setting the target temperature to either LO or HI will crank the blower speed all the way up.

If the blower speed varies for no apparent reason, I'd first rule out the regulator, before moving on to the CCU itself. BTW, autuhaus has refurb CCUs for ~400$ last time I check, way cheaper than the 2000$ quoted at the dealership.

It's a wonderfully complex system, which I've spent a long time figuring out.
 

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2000 C230 Kompressor Sedan
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42 Posts
You could try cleaning the knob with electrical contact cleaner as stated above. Usually however, what controls blower speed is the blower motor resistor. The knob/climate control just supply a voltage to the resistor, and depending on the input voltage the resistor regulates the blower speed. If the speed is changing for no reason I'd first suspect the blower motor resistor.

For those with the electronic automatic climate control, when the unit decides it needs a change in blower speed when in the automatic mode, it should display the commanded change in speed in the fan speed selection. The module decides on the fan speed depending on how close the target temperature is to the current cabin temperature. The closer the temperature is, the lower the fan speed, with a minimum of notch 3 (for those with the display type CCU, the older automatic CCU has less fan speed notches). Setting the target temperature to either LO or HI will crank the blower speed all the way up.

If the blower speed varies for no apparent reason, I'd first rule out the regulator, before moving on to the CCU itself. BTW, autuhaus has refurb CCUs for ~400$ last time I check, way cheaper than the 2000$ quoted at the dealership.

It's a wonderfully complex system, which I've spent a long time figuring out.
Hey Patman,

I, like so many others, seem to be having this same problem - though after my analysis (which I'll explain in a moment) I am pretty sure it's the actual fan motor control switch that's the problem on my car which has the manual heat/ac system.

Here are my symptoms: The fan speed fluctuates sporadically in the 1, 2 and 3 settings. Yet once on 4 or 5 the speed stays consistent.

Here's what I did: I noticed that if/when I press or wiggle/jiggle the fan control switch when it's in the 1, 2 or 3 settings, my manual manipulation of the switch causes an immediate change in the fan speed. So, it's for this reason (and based on my experience working with and repairing electronics) that it's more than likely a problem with the switch.

Here's what I plan on doing:
I don't think I wanna just pull the knob off and spray contact cleaner as I don't think I wanna risk a short in case it doesn't dry as quickly as I hope it will. So, instead, I'm going to remove the trim panel, get the switch out and do my best to disassemble it so that I can do a good n' proper cleaning of the internal contacts. That's if I can disassemble the unit. If not, I'll just take it out of the car and then I'll do the "spray into the shaft area and hope for the best" routing. This way the unit will be disconnected from the rest of the car's wiring - and I can let it sit on my bench for a good amount of time to allow it to dry out before replacing it in the car. This way I can also drive the car, with the control still disconnected and sitting home drying out, without being concerned about a short occurring.

BY THE WAY - A WORD TO THE WISE AND, IN PARTICULAR, ALL THOSE WHO DON'T FIT THAT CATEGORY:
DO NOT EVER.....EVER.... EVER.... USE WD40 AS A CONTACT CLEANER. THAT'S THE WRONG PRODUCT TO USE AS A CONTACT CLEANER. IF ANYTHING IT MAY WIND UP CAUSING MORE PROBLEMS IN THE LONG RUN AS IT LEAVES AN OILY RESIDUE - AS ONE PREVIOUS POSTER ALREADY APTLY STATED.

IF YOU'RE GONNA ATTEMPT THIS REPAIR, GO TO YOUR LOCAL AUTO PARTS OR HOME IMPROVEMENT STORE AND GET YOURSELF A SPRAY CAN OF ELECTRONIC CONTACT CLEANER. IT'S WORTH THE 5 OR SO BUCKS IT'LL COST, AND WORTH WAY MORE THAN THAT IF IT FIXES YOUR PROBLEM OR PREVENTS ANOTHER FROM HAPPENING AS A RESULT OF USING THE WRONG (I.E. WD-40) PRODUCT FOR THE JOB.

I'll post back after I've had the chance to get to this. May take me a week or two as my time is tight but I'll follow up when all is done.
 

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1997 W202 C220
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148 Posts
Hi, it will be nice if you can include pictures from how you disassembled it so we can follow correctly, thanks

Hey Patman,

I, like so many others, seem to be having this same problem - though after my analysis (which I'll explain in a moment) I am pretty sure it's the actual fan motor control switch that's the problem on my car which has the manual heat/ac system.

Here are my symptoms: The fan speed fluctuates sporadically in the 1, 2 and 3 settings. Yet once on 4 or 5 the speed stays consistent.

Here's what I did: I noticed that if/when I press or wiggle/jiggle the fan control switch when it's in the 1, 2 or 3 settings, my manual manipulation of the switch causes an immediate change in the fan speed. So, it's for this reason (and based on my experience working with and repairing electronics) that it's more than likely a problem with the switch.

Here's what I plan on doing:
I don't think I wanna just pull the knob off and spray contact cleaner as I don't think I wanna risk a short in case it doesn't dry as quickly as I hope it will. So, instead, I'm going to remove the trim panel, get the switch out and do my best to disassemble it so that I can do a good n' proper cleaning of the internal contacts. That's if I can disassemble the unit. If not, I'll just take it out of the car and then I'll do the "spray into the shaft area and hope for the best" routing. This way the unit will be disconnected from the rest of the car's wiring - and I can let it sit on my bench for a good amount of time to allow it to dry out before replacing it in the car. This way I can also drive the car, with the control still disconnected and sitting home drying out, without being concerned about a short occurring.

BY THE WAY - A WORD TO THE WISE AND, IN PARTICULAR, ALL THOSE WHO DON'T FIT THAT CATEGORY:
DO NOT EVER.....EVER.... EVER.... USE WD40 AS A CONTACT CLEANER. THAT'S THE WRONG PRODUCT TO USE AS A CONTACT CLEANER. IF ANYTHING IT MAY WIND UP CAUSING MORE PROBLEMS IN THE LONG RUN AS IT LEAVES AN OILY RESIDUE - AS ONE PREVIOUS POSTER ALREADY APTLY STATED.

IF YOU'RE GONNA ATTEMPT THIS REPAIR, GO TO YOUR LOCAL AUTO PARTS OR HOME IMPROVEMENT STORE AND GET YOURSELF A SPRAY CAN OF ELECTRONIC CONTACT CLEANER. IT'S WORTH THE 5 OR SO BUCKS IT'LL COST, AND WORTH WAY MORE THAN THAT IF IT FIXES YOUR PROBLEM OR PREVENTS ANOTHER FROM HAPPENING AS A RESULT OF USING THE WRONG (I.E. WD-40) PRODUCT FOR THE JOB.

I'll post back after I've had the chance to get to this. May take me a week or two as my time is tight but I'll follow up when all is done.
 

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'04 W211 E240, MY10 W204 C300
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825 Posts
Electronic componentry on the controllers at the back of the fan switch.
Unfortunately very common and a replacement unit is the best fix.
I have two cars with this issue.
Go to Pick a part and get a replacement. Make sure you get the right one for your car. There were various types.
No guarantee unfortunately - many cars have the same issue.
The regulator on the fan is another problem.
Early cars have the regulator behind the fan switch and not on the fan itself.

Remove the fan and clean up any oxidization on anything electrical you can see.
 
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