Howdy folks. I'm a long time fan of the site and you all. Usually, I find my answers by reading others threads... but now I've an electrically problem that I've yet seen addressed.

Blower doesn't run in my '91 300E (I know - not so unsual in itself) Untill last month, it was intermitant (would start sometime when I started the car with the switch on, but not at other times). Now it is no go 24/7.

The fuse has been checked and is good (flat strip external and in front of the fuse box).

Dug down to the blower. At first, it seemed a bad motor given direct contects to the battery didn't turn it, so I replaced the brushes and now it runs well when directly connected to the battery. (Honestly, I may not have tested correctly the first time prior to replacing the brushes, given a possible faulty lead wire used for the check). Anyway, the motor seems to work fine now.

Reinstalled, and still no go. (Even with temp set to low, and selection to EC Vent) Blower still works when direct to battery.

My voltage meter reads 14.06 V across the leads to the blower when the engine is on and either the high or low fan speed is selected. (With engine off, 0V. Battery w/ enginge on 14.15 V, w/ engine off 12.52V) (Haven't check the amps given the expected result is off the range of my crappy little radioshack multimeter, but it would seem with the voltage, I don't have an open circuit.)

I've check the conector behind the fuse box, and it is clean and firm. Honestly, I'm a bit out of ideas, and not looking forward to the expense of relacing random wiring harnesses until I find on that might fix the problem. Any thoughts on what else I should check?

-Jake in Sandy Eggo.

 

Sounds like it could be the blower motor regulator.

The blower regulator is connected to the main fuse box and ground. With the ignition switch "ON", the blower regulator is supplied with battery power. Depending on the function selection of the blower switch, the ACC control unit continuously sends a control voltage of between 0.4 to 9 volts to the blower regulator. As a result, the blower regulator supplies a current between 2.0 to 28 amps to the blower motor, regulating the blower speed.

With the automatic function selected, the control voltages are influenced by:
• The nominal and actual values of the interior temperature (via the interior temperature sensor and the temperature selector wheel).
• The outside temperature (via the outside air temperature sensor on the blower housing).
• The operating condition of the system (heating or cooling).
• The coolant temperature.

Hope this helps.

Here's a wiring diagram to help you -- sorry for the poor quality, but I think you should be able to read it.




[IMG]local://upfiles/5574/EBB7CAAD1EC342658A3B3CA12A7E0EE6.jpg[/IMG]

 

Thanks SL600_Cruzin!

Am I correct to assume what you refer to as the "blower regulator" is the same as the "blower control unit" on the diagram.

If so, is this unit located under the blower motor in the blower motor housing, or elsewhere (say near the blower switch inside the center console)?

Is there a way to test this unit for the DIYer? Or is it a matter of buying a new one, plugging it in, and seeing if it works?

Again, thanks.
-J

 

The blower control unit (regulator with heat sink) is located in the blower housing behind the blower motor. As a result, the blower control unit is constantly cooled when the blower motor is running.


To gain access to the current regulator, remove the blower motor with bracket and the mounting screws (arrows), pull up carefully on the housing.
Remove the blower control from the side.
Three nuts attach the current regulator to the heatsink.
Prior to installation coat the heat sink-to-regulator contact surface with commercially available heat conducting paste.

The bottom picture is the unit itself

Hope this helps

[IMG]local://upfiles/5574/6ADFD8C4F8D34C8CAB63D06014CDD3F2.jpg[/IMG]

[IMG]local://upfiles/5574/E10BF727D0C84F059F9ABC1493590750.jpg[/IMG]

 

Ah... the infamous 'porcupine'. Could I be lucky enough that this unit is repairable, or it is just a total replace item? And if the latter is it advisable to get a new unit only, or can I get away with a used one?

Thanks again!

And here I thought it was only BMWs who have "******" on the inside!

 

this is the common problem for E39 also.

 

Sorry, but I don't recall the w124 as having a blower regulator. I believe that the have a resistor block. My question is are you getting the 14V with the blower connected or disconnected. The w124 does sometimes melt the fuse contacts in the fuse box which is best remedied by fitting an external fuse holder in its place. I don't think that blower control units were used until the intro of the w202 (C-class)

 

sounds like there was a mixed up.

if jake was talking about the "fan" and SL600_Cruzin thought it as a "blower" which jake mentions.

there was indeed a blower regulator.

 

Ok maybe I didn't read the first post properly, and I see that there is an external fuse holder already fitted, but you can still measure voltage sometimes when there is resitance in the circuit. It needs to be tested with a load across it. Either a test light or reconnect the fan.

 

Nope, Sleepwalker, Cruzin seemed understand what I was asking about. I asked about the blower motor and that is what he advised about. (My fan reference was to me being a fan of you and he!)

Dondas asked "I don't recall the w124 as having a blower regulator. I believe that the have a resistor block. My question is are you getting the 14V with the blower connected or disconnected."

Blower disconnected. Was testing the red and blue leads going to the blower.

And further "The w124 does sometimes melt the fuse contacts in the fuse box which is best remedied by fitting an external fuse holder in its place. I don't think that blower control units were used until the intro of the w202 (C-class)".

No need. Late model W124 (like my 91' 300E) have an external fuse. For early models, after numerous reports of the #12 melting, MB issued Service Information Letter 54/13 (March 1987). They came out with a kit to separate the blower motor circuit to a 30 amp external fuse housed in a separate holder outside the fuse box. For more info on this see:
http://www.mbca.org/pages/tech/MBCA_blower_fuse_kit.htm

So far, I've pulled out the blower control unit (aka, blower regulator, aka 'porcupine' resistor). Found a lot of debris down there - leaves and oilly hood insulation foam from a lost oil cap related gusher several years back. Not a good operational environment of this heat sink! Suprised it lasted so long!

The control unit doesn't seem to be a repairable unit, and so far I've found no one who has attempted a fix it for it. MB want's >$300 for a new one, but various online sources have it for $237. My local "they pick" used parts place is offering one (untested) for $50.

I now see Dondas' rationale for testing the current in series prior to committing to replace the blower control unit, and may still do this. I'll let all know how she turns out.

Thanks all!

-J

FYI: if your reading this thread, I also found some useful information on this subject at a site by "those other guys" at
http://www.mercedesshop.com/shopforu...d.php3?t=98946