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Burning smell & black foam particles from AC

9K views 30 replies 14 participants last post by  43sqd 
#1 ·
Since I got the ML whenever the AC was on there was a strange smell, like something is burning & even the eyes were getting itchy..... The AC wasn't been used much so I ignored the issue, thinking I will look at it sometime.....
Today it was 40* Celsius, so I did turn the AC on. I was wearing a white shirt. The AC was on about level 4. Everything nice & cool. The burning smell started again. By the time I reached my destination my white shirt was covered in black particles & black dust. Upon closer inspection some of the particles were black foam/sponge pieces ,others were like plastecene (like the sponge was heated up till it melts).
I would like to ask what is going on??? Were is this sponge coming from & why(&were) is it getting burned/heated? Has anyone had a similar issue?
Thanks.
 
#3 ·
Art, It appears the insulation inside the HVAC duct work is coming loose and the burning smell is coming from the HVAC Blower Motor's speed control resistors mounted in the Duct work just before the HVAC Air filter (#47 below). The slower the fan speed the hotter these resistors get. At full speed the resistors are not in the motor circuit so there is no heat. The HVAC air filter should have filtered out these particles so I would start by removing and inspecting the filter located below the instrument panel and at the same time remove the resistor element which is easy to do. I would then vacuum out the inside for a temporary fix.

Now there are two speed regulators, #44 in the picture below which is the resistor heater type and #45 which is used on the later W163's. I don't know what year the cross over was made. The newer #45 may be electronic and not produce much heat. I'm sure the known experts will chime in here.

Mike
 

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#27 · (Edited)
Just got finished replacing these vent seals a little bit ago. HUGE improvement in the ability to adjust airflow to the vents. Should also help with directing more warm air to the defrost when you have the control knob in that position.

The instructions above are excellent and I had absolutely no issues replacing the foam. MUCH better quality than the original foam, which was pretty much non-existent after 15 years.

I started with the driver side single vent, then the passengers and finally the center assembly. Believe it or not, the center was actually the easiest, once you have it removed ! I found it helpful to warm up the ML and open the vents with full heat before I removed them. I did not have the proper plastic trim tool, but a disposable plastic knife worked just fine. One thing...on the side vents there is a seperate defrost vent that helps to clear the side windows. This is easily removed with the tool before you remove the vent itself.

Important to thoroughly clean the groove that the new foam will rest in. I found an old toothbrush (I never throw those away!), some hot water and a little dishwashing detergent did a great job on the old material. Its also a good opportunity to use some 303 or similar plastic protectorant before re-assembly.

All in all, this is a very easy project that gives amazing results and will be particularly beneficial with cold weather on the way. Definately a HUGE improvement !

Here's the fellow to contact for the vent seals :

http://www.benzworld.org/forums/252898-mbenz80.html
 
#20 · (Edited)
I'm the guy who used to sell them on e-bay but do to very little demand, I stoped re-listing them. Anyone here can PM me for new set. I have always send out 6 of them just in case one ripped in the installation process since they have to be stretched over the plastic window. Cheapest foam known was used on oem vent seals which will disintegrate quick & turn back to liquid or mud in no time. I'm maintenance manager for passed 15 years at foam converting and gasket die cutting factory. I made a steel rule die to cut these seals to fix my own. heck these pictures: vent closed but notice how much light/ai goes thru vent because the foam is already gone and you have little control over air distribution. I fixed mine 4-5 years ago and they still seal at 100%. Light in picture #8 is just a camera reflection. Check last picture with two vents in open and one in closed posiotion.
Burning smell could be short/worn brushes and dirty commutator in your blower motor if you can smell it at max. speed (#4 setting). Take it out, clean it and try it again. If the smell is in lower speeds, as previously suggested junk is glued on speed regulator resistors or they have bad/corroded connection.
Good luck, Bernard
 

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#24 ·
Springerfever I got your payment, they will ship out today and I will refund $2.50 to keep the old price for our forum members.
Noodles (you should be sleeping at that hour) :) stop by when you in Barrington, I'm one mile away and I wish to meet you anyways. Now I have two of them as you, 99 and 01 both 320s. Send me PM and I will let you know my e-mail address.
43sqd, reply to your PM was send out.
I will re-list them back on but have to do it all over again since it was not saved.
Bernard
 
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#28 ·
Thanks very much to Bernard for sending me a set of seals.

The one thing missing from the DIY thread instructions and WIS is this metal clip/bracket that presses against a hole in the underside of the center vent. In my case, the front end of the clip was poking up inside the vent, preventing removal after I had released the clips top and bottom. I had to insert a flathead screwdriver under the loosened vent to push the clip forward off its mounting.
 

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