Intermitent Blower Fan in Climate Control Mode (81 300D)
 

Recently the blower fan has been intermittently not starting in EC or the auto AC climate control modes. The blower will always start and run in defrost mode and sometimes when switching to manual operation. Running the defrost sometimes will get the fan to run in auto. From reading previous posts I suspect the issue is related to the blower fan controller module. Does this sound right? Where is the control module located?

Old Blower Motor
 

First thing to check is the blower motor's brushes ~ at this late date most are simply worn out and are not terribly hard to replace .

New fan motors are $!GASP from Mercedes but only $100 from Uro.....

I tried the junkyard routine, every one needed new brushes although they worked for a while .

I thought about brushes, but the blower will always run when switched to the defrost setting.

That's the # 1 indicator that everything _else_ is fine and the brushes are shot .

That's interesting. Can you let me know why that would be the case? Thanks.

Blower Motor Brushes
 

I knw this will sound lame but here goes :

All the older, mostly now long gone W123's Mechanics and Enthusiasts told me thus way back when I bought my first W123, save time they said, just replace the brushes first or the whole motor if you're rich (IIRC it co$t $1,500 then) .

So, I yanked it, took it apart and Lo ! the brushes were shot, $10 from M#rcedesource and it's been working fine ever since .

I'm now on W123's # 5, 6 and 7(keepers all I think) and all seven of them have needed fan motor brushes , some still worked but worked far better once i replaced the brushes .

Feel free to spend time doing other testing first, there's always something in the HVAC that needs tinkering, share what you learn .

If the fan runs fine on Defrost, the brushes are probably fine. Defrost puts the motor to default high-speed and bypasses the resistor assembly. If the brushes had problems, the fan would have difficulty reaching full power because it couldn't draw adequate current. Not saying it couldn't use new brushes, but they're unlikely to be the problem.

There's likely an issue with poor soldering on the pushbutton unit, a poor connection in the switch box (module behind the glove box), or a problem in the resistor unit.

If you push the switch to Max fan and it still doesn't run like it does in Defrost, the problem is probably in the pushbutton unit. The Germans didn't seem to know how to make electronics with good solder joints in the 80s. I can't even count how many intermittent frustrating problems I've fixed in my 2 just by resoldering control modules.

Taking The Long Road
 

O.K., do it the hard way, let's see if you admit it when you're finally done .

Or maybe listen to someone who actually services DC motors for a living. Checking the brushes is fine, but if they're not worn completely away they aren't the problem.

[QUOTE=Diseasel300;3835695] There's likely an issue with poor soldering on the pushbutton unit, a poor connection in the switch box (module behind the glove box), or a problem in the resistor unit.[QUOTE]


They made sure to have enough distributed components in the system, the pushbutton control, the fan speed (resistor) controller, the resistor and I think a temperature controller and the sensor.


I had the pushbutton unit re-soldered a few years ago, but I'll take a look at it again. Is the fan speed controller acessable by removing the glove box? I recall the temperature controller was inside of there.

It seems that the issue is not that the blower fan will not run at times, its the delay time before the fan starts in Auto. I find if I wait it will always run but sometimes it takes a while.

So supposedly the 1981 300D can come equipped with the old Klima A/C servo and 'computer' behind the glove box.
If that is your case, check the 'computer' behind the glove box lining. It a square looking thing. If it has dark burn marks visible the swap a decent junk yard one in for a test...

Can't hurt. It might affect your blower functions...maybe not. my 2 cents

also this thread might have tips
http://www.peachparts.com/shopforum/diesel-discussion/309358-1984-300sd-blower-failure-odyssey.html

Servicing Electric Motors
 

O.K. then, recently there was some commenting on the best ever electric motor lube, can you tell me what it is ? .

TIA,

-Nate

For small motors, you can't beat Zoom Spout Oil. It's the correct weight, correct grade, and correct type of non-detergent oil designed explicitly for electric motor bearings and sintered bronze bushings. Don't lube the commutator.

No, its a system with the later climate control & monovalve. There are two control boxes in the area in back of the glove box, one is the temperature controller and the other switches the blower resistor segments.


I wonder which if any of the controls the time delay for the blower to run.