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Read through the entire post. Likely cause is the fan speed control knob. May just be dirty and possibly cleaned to fix.

Good luck! My 99 c230k started doing same in position 1-3 after replacing failed fan(and regulator).

Will attempt to clean when I get a chance.
I took the knob out, used contact cleaner. Now everything works perfectly
 

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C200 Classic 1997
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No sir,
Behind the fan speed control nob is a single 4,7 kilo ohm (I dont see any electrical simbols on my phone) variable resistor or potentiometer that I replaced.
I purchased 10 as its cheaper to purchase a standard pack of 10 than getting one or two plus the postage .....

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Hi Alf, can you please post a photo of the resistor that you are referring to? Is there only one or two? My fan started to run at different speeds on the same setting, now it sometimes only runs on slowest speed irrespective of the speed control setting, then it comes right again after the car has been switched off and is restarted. Sometimes it does not respond to speed settings, then it will revert to slowest speed when the knob is adjusted - very erratic. Initially it responded well to cleaning with contact cleaner spray, but that remedy no longer seems to make any difference so perhaps the resistors that you refer to are the problem.
 

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Try pushing and pulling gently on the fan speed control knob when it starts to do intermitting, if moving the knob affect the speed and you feel it then it should be cleaned, sometimes knocking on it will change the speed too.
When I had the problem, I replaced the resistor, the blower and many other small parts. Nothing helped, you could try, your case might be different, for me the only thing that did work was taking off the knobs and spray the inside with electrical contact cleaner, leave it over night and try it in the morning. You can use WD-40 electrical contact cleaner or CRC. they both range between $6 -$8.
Hope that helps.
 

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C200 Classic 1997
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No Frans this is not it. This is the motor resistor, the one I am looking at is an electronic unit that sits behind the speed control knob in the centre console. See Alf_Hockley's post above.
 

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C200 Classic 1997
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Try pushing and pulling gently on the fan speed control knob when it starts to do intermitting, if moving the knob affect the speed and you feel it then it should be cleaned, sometimes knocking on it will change the speed too.
When I had the problem, I replaced the resistor, the blower and many other small parts. Nothing helped, you could try, your case might be different, for me the only thing that did work was taking off the knobs and spray the inside with electrical contact cleaner, leave it over night and try it in the morning. You can use WD-40 electrical contact cleaner or CRC. they both range between $6 -$8.
Hope that helps.
Thanks
 

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I have had also problem for over a year now where the speed of the fan is jumping irregularly and I have also noticed that wiggling the speed button adjusts the speed. I also ran into conclusion that possibly the contacts have somehow oxidized. So I just tried cleaning mine some minutes ago, attached couple of photos from the PCB's. I did not want to detach the bigger pcb of the buttons completely so in the end I just sprayed Electrical cleaner to the connections of the speed potentiometer and also the heat regulators as I've had some problems with the heat only being constant on the max heat position which makes the cabin too warn in a long run. I have yet to attach the AC unit back to my merc and then to see if this did anything. Thanks for your posts so far, I hope the described method also helps in my case. Also a word of advice to other people possibly taking their own units apart. When opening the casing of the unit, do not use excess force as the two pcb's are attached to each other by connector/pin setup, dont know the proper word for it. But anyways try to take it apart so that both edges are opening evenly so that you dont end up braking the connector pins. I found this video to be of great help when removing the AC unit from dashboard. I did not go all the way to remove the other parts as i have the casette holder and was not successful in removing it so i just ended up opening the other pieces in the dash so much that i could take out the ac unit. I also kept the other cables still attached to not make any error codes.
2622945
2622946
 

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w163 02 ML500 W210 97 E50Amg w202 99 C230K w124 - need more space, time to build again
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Great YT post Marsumein. Welcome. :)
I saw this awhile back.
Good info to know.
 

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I reinstalled the AC unit yesterday and with short testing atleast the speedcontrol wasn't jumping anymore when jiggling the button. The car's for sale anyways so possibly I will not see if it is a longterm fix.
 
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