The blower stopped working on my 300D. It's a 1980, so it has the servo.

How things unfolded:

First the blower would _not_ shut off, despite pressing the off button. This lasted for a couple months, although I only drive the car sporadically.

Then, over time, the blower would come on only briefly (a few seconds while driving) then shut off.

Now I get nothing.

I don't see any disconnected vacuum hoses in my initial investigation, though I have not made it behind the push button unit yet.

I should note that when I run the car and push the def button that although the fan does NOT come on, I can hear the servo working. I can also see the vacuum pod behind the glove box respond to the pushbutton unit with the car running.

Where should I go from here?

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E

I have the same car.

Those evil servo systems are trouble. I replaced my servo in 1997. It went bad again two years ago. I just wired closed the hot water valve on the firewall and run the a/c on defrost. (The temperature never gets below 65 degrees here.)

The problem you are now having sounds strange. The defrost button by-passes everything. The blower should run on defrost regardless of relay or vacuum problems, unless your push-button control is acting up or power is not getting to it.

Your previous problem of intermittent blower operation sounds more like evil servo or vacuum problems. Those old vacuum lines get hard and crack. There are a bunch of vacuum operated solenoids and switches under your dash that control the climate control. It is a complex system. Not rocket science, but the circuits do require some study to understand. And you have to remove the dash to get at all of those vacuum lines, solenoids, and switches. It is not a one week-end job.

Unlike the W115's, the W116's, the W123's, and the W124's were a rich man's car. And those Chrysler evil servos were even worse than those diesel engines GM put in Buicks and Oldsmobiles in the 1980's. (If that is possible.)

Richard

As it's a 1980 model, the blower's brushes have prolly worn out .

About $15 for a kit from M erced es S ource in Bellingham, Wa. for two new brushes and instructions, it's a fiddly job, i always clean every thing and use a precision (needle typ) oiler to lubricate the two bearings whilst it's apart .

Uro brand sells them new for $100 list price, works the same but noisier for some reason .

Don't waste time on junkyard used, it'll work a while then poop out again pissing you off .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thanks, VWnate, Rasper.

This is my second time around with the servo. It's actually worked since about 2004, so I guess that's not too bad. The unit on my 116 car failed about one year after I got it, so I bypassed it. But 300D is a keeper and I think I'll take the time to fix it properly, especially as the car is not needed for daily use.

https://www.ebay.com/itm/MERCEDES-HEATER-A-C-SERVO-UNIT-REMANUFACTURED-WITH-NEW-ALUMINUM-BODY/263304177088?hash=item3d4e26e5c0:g:hEgAAOSwn7JYCoCm&vxp=mtr

The seller above has a reasonable price and solid feedback, so that is an option if the servo turns out to be the problem. Or the digital version that came out a few years ago, if those are still around.

But I will start with the brush kit from MS, as Nate suggested.

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E

That's interesting, looks O.K. and I like the silicone gasket idea .

It's very important for _you_ to test the unit before installation, the servo needs to operate fully and stop at the end of each direction with a *thunk* not slow down and stop .

It's adjustable and about 1/2 the servos I got would do the slow down to a stop thing in one direction, this is what causes the little amplifier thing behind the glove box to fry .

It's also critical to maintain the entire cooling system clean as a whistle ~ when you remove the radiator cap there must be ZERO crud or red/brown silty stuff anywhere .

Use the citric aid cleaner to get everything clean and then use proper coolant and distilled water mix (60 % water, 40% coolant) and change it every 12 months regardless of miles, you'll have a trouble free Klima I HVAC and ice cold Air Con to enjoy .

A tiny bit of silt or crud is all that's necessary to kill the servo and when it dies, the amplifier goes too .

New servos are still made in Mexico by/for Mopars, much cheaper, aluminum bodies and decent quality although they often need that final adjustment before fitment .

I learned all this the hard way and now choose to have only manual or Klima II equipped Mercedes' .

I understand having a keeper, IMO once you find the one you really like, stick with it and enjoy the miles as they roll on by .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

The suggestion to install new brushes is a good one. What I found was that my brushes had some life left but the commutator was filthy and pitted badly. I cleaned that up by chucking it in an electric drill and using sandpaper.

Brushes would explain the blower not running and also cutting off after a few minutes, but not the previous condition of not turning off.

Still, VWNate is right on. After almost 40 years it's probably brush changing time.

Richard