'75 240D - The Heater Blower

[TylerFrank]

Well, it looks like time has taken it's toll with my heater blower, which I've read is one of the most inconvenient and anger-provoking repairs for this model.

Bummer.

See, I live in cold snowy Minnesota, and heat (especially heated defrost) are sort of essential. So I'm willing to dive into the the replacement (which ring of hell is that in again?).

Anyone know where I can find a detailed walkthrough, or at least an explosion of the things being dismantled? I've heard this can take up to 20 hours.

Does anyone here want to give me a broad description of what needs to be done? Do I need to tear the whole dash apart or what?

[79Mercy]

here ya go.

http://www.ramdesign.on.ca/pdf_files/blower-install.pdf

I need to replace it in my W115 but I dread taking everything apart.

[diametricalbenz]

Wow that really is a huge pain for the blower. I just hope mine holds out long enough. But at least one nice feature is the vent function that is proportionate to vehicle speed.

[TylerFrank]

Well thank you, sir!

Man, I wish you would have responded sooner - before I agreed to pay a mechanic on JustAnswer.com $30 for help. He gave me the same exact link.

You wouldn't happen to be Marty, would you?
; )

[Eirik 400 SE]

It sounds like a big job when you see it like that..
But in short form:
-Remove grille in front of windshield, and disconnect electric connector
-Drain fluids and disconnect all 3 hoses
-Remove centre console and both front carpets.
-Loosen both rear-heating ducts, unclip bottom half of blower cabinet.
-Disconnect the control-rods to the housing, and the side-ducts from the housing.
-Remove the centre duct screws and disconnect the internal rod.
-Remove the complete housing ..
-There you have the fan.
-Done..

But check to see if the fan is the problem. Measure the voltage coming out of the dashboard-switch, check the resistor on the ventilation-chamber, connections and the knob in the heater-control..

[TylerFrank]

Originally Posted by Eirik 400 SE

But check to see if the fan is the problem. Measure the voltage coming out of the dashboard-switch, check the resistor on the ventilation-chamber, connections and the knob in the heater-control..

What do you mean by the dashboard switch? I assume it's different than the defrost knob, because you mentioned that also. I checked the voltage to the relay in the firewall and it's definitely getting power there, but you're mentioning other parts...

Anything you can give me to troubleshoot would be greatly appreciated. I'd hate to tear this thing apart to find out it was a simple connection failure.

[Eirik 400 SE]

Ok, will try..
Do you have AC in your car ?
I must ask, since you refer to defroster as a different thing..
In my car there is only 1 knob and 1 fan-motor.. But, I belive that the AC-equipped cars have an extra fan...

This is a pic of a dashboard with heater/defroster only..
If you have AC, then you should have an extra switch in the centre-console too..

There's a connector on the firewall.. Start there..
Disconnect, find ground.. Connect to a multimeter.. And see if the power comes through to this coupling.. There should be power coming through every single one of the other connectors, depending on wich "level" you set the control-knob in..

If you check this page out..
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Pic no 1. pos 17 is the heater/blower.. Or maybe you call it defroster !?
No 21 is the resistor-box that fits inside the chamber in front of the windshield. The contacts on that, is coming into the engine-bay .. Where you disconnect the plug.

If you check this pic out.. then you see the additional AC-fan and other components.
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Fan no. 17 in the first link, usually stops working after xx years.. Either because of worn-out sontact-points, or due to dust or also maybee water has entered the fan-motor due to clogged draining holes..

If you have AC, then the job of reaching the fan(17) is a bit bigger and more difficult I guess. And then I can't help you with the AC-parts..

Some fans, only need a tiny push in either direction to start working again.. Thay can stop "between tracks" if not used often enough..

But, check the connector-plug at the firewall..
If the power reach this point, then it's either the resistor-box, or the fan itself..

If there's no power there, then you might want to check the connections in to the knob in the middle of you dashboard.. (The knob for the defroster.. )

[TylerFrank]

I do have A/C, and in my understanding they have separate fans, which is also shown in the second parts explosion (cylindrical canister style rather than axial, right?)

I checked the plug in the firewall leading to the resister, and I believe there was power to it. I'm not real experienced using a multimeter, but here's what I did: Set it to DC and stuck the needles in all combinations of the 4 female jacks on the plug. I got a reading on 2 combinations (jacks diagonal from eachother): 12.8V and -12.8V, which I assume are the same reading in different directions. Is this the right process? This is a pretty basic thing, I know, but I've got to start somewhere.

I saw someone say that I could take a straw-full of ATF and drop it into the fan, then give it a little shove and see if it fires up. Probably a good idea before spending upwards of $100 and 8 hours on replacement, eh?

[Eirik 400 SE]

Measuring sounds ok.. Try the 3 points.. There's 1 ground and 3 different fan speeds, so turning the knob inside should move the power to another point..

Not easy to hit the fan-motor.. And then there's the not so nice smell of oil !?
But, taking of the "grille" in front of the windshield will give you access..
Try to give a small spray of som penetrating oil onto the fan.. Let it sink in..
Then carefully try to move the fan-blades...
If it turns, then It can be the contact-points or the resistor.. Usually only step 1 of the resistor burns out.Wich means 2 and 3 should be fine..

[TylerFrank]

Ha, that makes a lot of sense, doesn't it? Three speeds = three connections and a ground. Duhr. I'm learning, albeit slowly.

Thank you very much, sir. I'll keep up to date when I get time to dink around.