Hi Everyone, I need to get to the bottom of my blower woes, as I can no blower activity at all in my 75 300D.

I have taken off the center console and exposed this blower that blows air by your legs. I have been told this car has two blower motors.

Is there another blower motor behind the insulation that blow air into the side ducts and windshield vents?

Also, I noticed that when I turn on the blower switch, I get no current reading at this blower motor. I assume this means that the problem is with the other blower motor which feeds the current to this one?

Thanks.

Mark

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1975 300D

The blower in the picture is the AC blower. In the box forward of the blower is the
AC evaporator. The heater blower is hidden up near the windshield just below the cowl grille where it is nearly impossible to reach. I owned a 1975 240D years ago and discovered that there is a switch that is operated by a vacuum pod located just above the accelerator pedal that switches current between the two blower motors depending on the position of the AC temp knob. When the AC temp knob is all of the way counter clockwise, the vacuum element will change the vents to fresh air and switch to the heater blower. When moved clockwise the vents change to recirculate air through the evaporator and switch to the AC blower. If this switch is not adjusted properly,the vacuum pod not working or the switch broken, one or both of the blowers will not work. Hope this helps.

Thanks for the info. I took out the AC blower and it works. I hooked it up to power and it spins. But no luck when connected into the system.

I tried to spin the heater blower with my hand and it barely turns. So I take it that the bearings seized or something. So how do I remove it? Does it come out by the cowl grill?

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1975 300D

I was lucky enough that I didn't ever have to deal with the heater blower when I had my 115, so I don't have a clue as to how to remove it. I sold the car in 1996, so I don't any longer have access to the car or the manuals. Others on this forum have said that it is very difficult, maybe someone who has done this will post the instructions. I do know that when the system is in the heat mode, forward motion of the car often gave enough airflow that I didn't need to use the heater blower except for quicker warmup or defrosting. Sorry that I can't be of more help.

Before you even think about removing it.... have you put juice to it to make sure it doesn't respond?
There is a connector in the dash---- black plastic with about 8 plugs on it. Open it up and tinker with it... with a wire.... I forget the connections but try all possible combinations... you may get that blower motor to spin. I did. After I had taken the whole darn thing out. and it worked! I wish I had done this first and saved me the trouble of removing it.

The Chilton instructions (already posted elsewhere for you) say:
1. Remove blower motor cover.
2. Remove blower motor.

They leave out one important step which PRECEDES steps 1 and 2 above:
1. Remove entire car around blower motor.
Then proceeed with steps one and two above.

I recommend doing everything possible to connect/test it electrically before deciding that it is defunct. The real problem is often in the wiring circuit/diodes/resistors, etc., not the motor itself.

Good luck.

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[SIGPIC]
Tom
SE Connecticut
1975 W115 300D

visit my blog:
http://mercedesdieselrebuildingdiederich.blogspot.com/

Tom, how do I get access to the blower motor wiring harness? Where is it? And since the fan blades don't want to spin, as they should, is that not a sign that the bearings are seized?

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1975 300D

I would not conclude that the bearings are seized just yet.

Find that plug in the console. I pulled it apart and tested all possible circuit connections. There are a lot of possible combinations. In my case, sure enough, I got the motor turning. So I just hot wired it right there. you will need a jumper wire to do the testing. Hit every possible combination before you decide that the motor is dead. It surprised me.

If the motor does turn, the proper way to do it is to further trace the circuit to the resistor that is probably the problem, at least in my case, since the motor works fine when it has juice. I don't know about yours, you will have to test to find out for sure. I never did that, since I got it working adequately.

Be careful not to jump to premature conclusions.

What reference manual are you using?

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[SIGPIC]
Tom
SE Connecticut
1975 W115 300D

visit my blog:
http://mercedesdieselrebuildingdiederich.blogspot.com/

Tom, I have no reference manuals.

My question is simply how does one access the heater blower fan? In order to check electricals, I have to get my hands in there. Even the wiring for the temp knob, which is right out in front, is almost impossible to examine as the switch assembly is riveted to a huge contraption which, to remove, has several mechanical linkages with clips that will be impossible to put back once popped out.

That switch could be the problem but I can't examine it. As far as the wiring harness for the heater fan, I can see no wiring for it as I can can barely see the fan itself. So I need to get access to the fan to check the wiring.

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1975 300D

1. I have removed that huge contraption and replaced it. It is not that bad of a job. It is easily replaced the same way it came out. I have done it several times now, and I have a spare unit. Just pay attention to the various linkages. It is not rocket science.... it is pretty simple. Put it back the same way it came out.
2. The heater blower fan cover can be removed... it has a number of clips holding it in. I removed my radio speaker in the dash to get access to the difficult clips. Once you remove the cover, it is easy to take out. The cover is the hardest part.... and getting it back together correctly.
3. Trace the wire from the switch to find the connector plug. It is there. I doubt the switch is the problem.... I am betting on the resistor/diode, what ever it is.

4. You need to get some sort of reference manual.

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[SIGPIC]
Tom
SE Connecticut
1975 W115 300D

visit my blog:
http://mercedesdieselrebuildingdiederich.blogspot.com/

In the vintage forum, I found this thread requesting a wiring diagram. One of the replies has a link to a pdf file that might help you. The edges of the pages are cut off, so not all of the circuits can be seen.
75 240D A/C wiring (W115)

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Gary
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1983 300SD