87 300D Blower Problem - PeachParts Mercedes-Benz Forum

Jmana · #1 07-17-2006, 07:27 PM

The forcast is calling for near 100 degree weather all week, so what more of a perfect week for my blower to stop blowing?!! Ever since buying the car, the blower has not been consistent, it would mostly blow slow, with the occasional burst of fast air, which didn't seem related to the speed of the car or the speed of the engine. So today it just quit altogether, with an occasional whisper of air that blows out just to tease me

Does this mean the blower is shot, or does it mean something else? I was ready to dig into the blower, but then remembered all the things that I have wasted my time trying to fix on this car, which had non obvious causes to the problem.

Jmana · #2 07-17-2006, 09:49 PM

I have one more thing to add that may help with diagnosing this problem. When I first turn the fan on, it will work for a couple of seconds then slowly die. Does this sound like a bad blower, or resistor, or something else? Please HELP!! It's hot out!

dieselmania · #3 07-17-2006, 10:35 PM

Actually the blower is easy to remove, it is located in front of the windshield, you remove it from outside. Why don't you open it up and run a hot wire to it to check it? Also, you might have a poor grounding connection. You could try running a ground wire to the metal part of the case to check that. When mine went, first it moaned a lot for about a year. I finally yanked it and replaced it with a new one, was close to $300 I think.

lrg · #4 07-18-2006, 02:09 AM

As dieselmania said try to "hotwire" it first to see if that's the problem. If it's still acting up before you replace it try partially dismantling the blower housing and try to coat the bearings with some oil. I wouldn't spray in WD40 unless you want to smell it for about a month. I used a short length of acquarium hose connected to a can of 3in1 oil and squirted it into the bearings at each end of the shaft by the motor. It helps to spin the blower a bit as you oil it. This rescued my blower, at least for now (about 18 months and counting).

Jmana · #5 07-18-2006, 06:58 AM

If the resistor goes bad, would it cause the same symptoms? Where is the resistor anyway? Is it possible to completely bypass it?

Jmana · #6 07-18-2006, 06:14 PM

Is it possible to run a "hot wire" to the blower without taking everything apart? I see a bunch of wires coming from the area where the blower is supposed to be, but not sure if they go straight to the blower, or which ones do so.

dieselmania · #7 07-18-2006, 09:10 PM

I can't answer your questions since it has been a while and I don't remember the connector. Plus I'm now 50 and suffering from CRS (cant remember s***). Plus all my manuals are at my buddys shop along with my 124 getting dash pods replaced.

Jmana · #8 07-18-2006, 10:20 PM

I see you have the dreaded #14 head too. Mine has over 260k miles on it, so I drive around with my fingers crossed

So you think there is a connector for the blower that I can tap into? That would be great, because I'd hate to take everything apart and waste a couple of hours, only to find out the blower itself is fine. But the more I think about it, it seems as if the brushes are gone. If that is the case, does anyone know where to get replacements, and how to switch them out?

brabus · #9 07-21-2006, 02:18 AM

any update on this issue. I would also like to know how to hot wire the blower.

Jmana · #10 07-21-2006, 07:11 AM

From what I have found researching this, there are 3 wires right above the brake booster near the firewall. If you ground the dark wire, it bypasses the resistor. I don't know if that is correct, but I tried it and still the blower is flaky. It sometimes works, sometimes doesn't. Guess I'll have to rip into it this weekend. I don't see the point of this resistor, if I find it is bad, I might just try and rewire it to permanently bypass it. Definitely cannot afford a new one.

DrLou · #11 07-21-2006, 12:14 PM

Jmana,

Don't know the 'D' model, but in the SDs, the blower motor and fan are under the right side knee bolster - behind the glove box. Very, very easy to clip a few pigtail connectors on the fan's contacts, easily exposed by pulling the plug. Is the layout on the Ds very different?

A couple of points: From what I've gleaned, these motors are rated to pull up to 18 amps at the absolute max speeds. In practice, mine pulls under 5 most of the time. As a precaution, while I was in the 'thick of it' with my ventilation system, I put a fuse 'in-line' with the fan to isolate its problems; in one case, it seemed that a dying fan had overloaded and burned the pushbutton control unit. (Though I am not throughly convinced of this to this day). Which brings us to the pushbutton control unit (PCU):

Have you considered that you may have a screwy PCU? In normal 'automatic' operation, of course, the fan speed may vary considerably, under control of this unit. If the fan speed is varying at all, then I think you can probably rule out bad brushes on the motor (a common problem, fixable for about $10 and some patience).

But it's easy (on the SD, at least) to pull the entire fan/motor assembly for inspection/testing. Put your ammeter in line to test the load. If the motor is 'going bad' - bad bearings, inadequate brushes - it will draw excessive current.

Curious to know your resolution. Lou

dieseldiehard · #12 07-21-2006, 03:47 PM

Don't listen to any other advise from a SD chassis owner, its confusing to say the least and not applicable!

The '87 300D's fan is up front under the cowling on the firewall. Under the hood.

And the '87 has a fuse on the L side near the strut mount, under a small plastic enclosure all by itself, its a strip fuse like the Glow Plug fuse but only 15 A IIRC. Check the fuse before trying anything. A cheap and easy fix if its bad. O/W you are into a big troubleshooting job (or shotgiun approach).

The push-button Climate Control Unit in the 124 is supposed to have current limiting incorporated into it, not the little relays that go bad like earlier models n the 123/126 cars.

The fuse is supposed to prevent the circuit traces from burning off like they did in the earlier 123/126 chassis units.

BTW the CCU in the '87 300D must be p/n 124 830 1885, the ones from 300E etc. are a different p/n so don't stick the wrong one in there and expect everything to work right.

There is a regulator module that controls the fan speed in the 124 diesel, it uses solid state (transistors) to control curent, NOT resistors.

Its a triangular shaped thing with fingers on one side (heat sink) and pretty pricey too, so don't mess with it trying to short it out! Just apply dc directly to the fan and if its not working right its the brushes in the motor. Getting to it is no fun!

brabus · #13 07-22-2006, 04:24 AM

I think this along with some other searching i did last night should help me get my blower going again, or get me to the point where i have to sell all of my blood for a week to buy a new part.

Jmana · #14 07-22-2006, 12:51 PM

Well, I got to the blower motor finally. I found the directions on this site to get to it, and it's not hard, just frustrating because all the plastic parts are fragile, and the clips that hold everything together kept falling off and down into the "Black Hole". Anyway, I took the motor out, and everything spun freely, and there were still brushes left. So I hooked it up straight to the battery. Don't know what happened there, but the positive wire immediatly burned off at the terminal, and the motor spun and almost flew out of my hand (didn't realize it had that much torque!). So then I figured I better strap it back in and hotwire it that way, but before doing that I hooked it back up and got inside to turn the fan on to see if there was any obvious reason as to why it would run for a couple seconds and shut off. Well I did so, and it ran for about 4 seconds the way it usually does, with it going fast then slow then fast, but then it just held steady at fast and continued to run. Went in, shut it off, and tried again, now it came on fast and stayed that way. Don't know, but I am thinking maybe the terminals were too corroded (the ground terminal was pretty bad). So I cleaned off the terminals, oiled it up, and put everything back together. One thing I did do before putting it back, was I hooked a wire onto the ground terminal, and routed it outside of the box, this way if it does act up again, I can easily ground out the motor and see if the motor is bad, or the regulator (essentially the regulator controls the ground going to the motor, the positive wire is always hot). Also, this is a great time to clean out the drains attatched to the outer plastic "troughs", both of mine were clogged. I had a little drain cleaner thing (like a brush on a 3 foot flexible wire) and with that and a hose I got them flowing again.