Brianarb

Hello, I recently purchased a 1997 s420. This is my first w140, but I have owned about a dozen other Mercedes, from a number of w123, w116, w203, w116 and w204 models.

Everything worked fine on vehicle until this morning. In a bit of a pinch at this moment as I work in the city and the car is currently there. I was driving with climate control in automatic position, AC cranking, smoke started to come from the dashboard and out the center dash vents. Smells like burning electrical insulation. Nothing stopped working with the climate control, but I immediately turned it off. I immediately pulled off to investigate but could not locate the source. Does not appear to be coming from the engine compartment, however.

I have read that the blower motor resistor gives problems. My goal is to get the vehicle home to further investigate. Other than taking off the paneling to disconnect the blower motor resistor, is there any other way to disconnect this by pulling a fuse? I located a 15 amp fuse for climate control, but there does not seem to be a specific one for the blower motor. Any help most appreciated.

Thanks,
Brian

Brianarb

No one responded to my post, but I figure I would provide an update: I ended up having the car towed back home. I used my electrical tester to check the blower motor, which seemed to put out a consistent 6 volts. The wiring did not appear to be fried. I checked the alternator output at the battery which appeared to be a consistent 14.4 volts. I ran the car for awhile, and the symptoms did not reappear. Everything seems to work fine on the car. I am planning to replace the blower motor resistor and cabin filter just in case. I will, of course, keep a fire extinguisher handy in the car.

I am officially otherwise stumped at this point as to what else the smoke could have been.

Brian

Russell Ormerod

maybe it was not smoke. maybe just mist from AC. smoke means a short. and that would be a major job to fix burnt wiring on a w140. better hope it's nothing

burgca

Brian unsure of the source of the issue, Mercedessource has guidance but normally the blower stops working, unusual to have it smoke
https://mercedessource.com/store/w14...r-demand-video

Good luck and post your findings

Brianarb

Thank you to those who responded to my post. As an update, I pulled the driver's lower dash panel along with the glovebox on the passenger side and did not find anything melted. I pulled the evaporator temperature sensor to see if that was the culprit but it looked fine. I pulled both the radio and climate control panel from the dash and did not see anything melted. In addition to testing the voltage at the battery, I looked at the wire from the alternator, and it appeared to be okay.

I replaced the blower motor resistor, along with the cabin temperature sensor fan located in the interior light/sunroof switch panel (it was buzzing). I think that this may have solved the problem as I no longer smell such a strong burning odor. Prior to replacing it, I noticed that the air from the blower motor was weak. It has certainly made my AC work much better. The fan moves much faster.

Brian

burgca

Glad you didn't find anything melted or fried. I changed the temp sensor fan last year as the noise was an irritant, but as you noted I have noticed an improvement in a/c comfort on auto without making any changes to the system.