w124 blower motor inop
 

Hi everyone. Today my blower motor decided to take a crap, the compressor still spins, but the fan will not work at anyspeed. I assumed the worst so I removed the motor and tested it. It works fine. Finally I checked the firewall connections. I'm not getting12v at the firewall connector or at the 30amp fuse strip (which is good btw). What gives? What provides the 12v to the firewall connector?

Sorry everyone 1987 300d

EPC
 

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"Quick and Dirty"
Do an Advanced Search (On this Forum)using Arthur Dalton's name as "Member".
He's dealt with all these Blower solutions,in multiples.
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As In:
Here's your assigned reading for the rest of the Weekend.
PeachParts Mercedes ShopForum - Search Results

But, this is the Electron Path you want
 

(As Always, Thanks Arthur!)

Also
 

http://www.peachparts.com/shopforum/tech-help/241868-95-e320-no-blower-speed-ccu.htm

[The 30Amp Aluminum Fuse @ the Strut tower (Driver's side) Looks can be deceiving !]

30A fuse feeds the Red wire @ the Firewall and if the fuse has a "Micro" (Almost invisible) crack ,no Power
@ red wire.

BTW, I also replaced the ignition switch 2 weeks ago.

Ok, just in case I wasn't clear (because I probably wasn't). Fan stopped working today. Ipulled the fan out and tested it by going direct to batter and it spins. I found that the firewall fuse had 0 volts on either side. I found that the firewall conenctor to the fan has 0 volts to the black and red wire. The yellow (which I assume is the signal from the HVAC unit) has some voltage nowhere near 12v. IF I disassemble the connector, plug the yellow wire into the firewall connector and give the black and red seperate ground and +12v my volt meter shows anywhere from 11-12v (depending on high/low selection) at the fan connection. About two weeks ago I replaced the ignition switch with a beck arnley unit.

Totally remove the above fuse and see if it stays in one piece. If it does not then you have found your issue.

Second Line
 

in reply #3

"Battery/Ignition Switch/F15-30Amp fusible Link/RED wire of firewall connector."

1.Arthur is your "Guide".
2.I've "Schooled" myself,in almost Pavlovian Fashion,to Only accept Empirical
results in Testing.(Provable,Repeatable/Infinitely)Through my own "Assumptions
Proving Incorrect and therefore a self concealed Trap to diagnosis.
3.YOU may have replaced the Ignition Switch (correctly) or had a "Wrench"
replace it for you(Possibly Incorrectly).Or the Ign. Sw. MAY be bad.I don't
know and it doesn't matter.

Testing is simple in this instance:
1.12V (Or whatever "Battery Voltage" reads) @ the Pos + Neg poles of the Battery ?
2.12V at the appropriate terminals @ the Ignition Switch ?
3.12V at the Red And Black terminals of the "Firewall" connector?
If 12V NOT present @ the required location,THEN you have to look
at the WIRING as a possible culprit,IF 12V IS present ONE STEP Back.

We usually avoid testing the Ign. Sw. in this instance if at all possible,
'Cause it's such a Pain to get to.AND Instead use the Firewall Connector
as a Surrogate.(If Voltage is present @ F.C. ...If MUST be present at the
Ign. Sw.)

The Yellow Wire @ the F.C. has it's VOLTAGE changed Up and Down by the
C.C.U. (Climate Control Unit) as a signal device to the Regulator for Blower
Fan SPEEDS.

The Wiring diagrams and schematics are always a great help to me in visualizing
the circuits.[on the Factory Service Manuals]

So
 

What was the Problem ?

Thanks!

Well my new ignition switch has failed. There is no continuity between either of the #30 connections (which is constant 12v) and 15x (which apparently is what goes throught the 30amp fuse and fan connections). Now if I could only source a decently price ignition switch that isn't BeckArnley.....

On the positive side it now only takes me 1 hour to r&r the ignition switch. Hint, I superglue the screw onto a little straight screw driver and start with the upper screw hole first.

No, Thank You!
 

"On the positive side it now only takes me 1 hour to r&r the ignition switch. Hint, I superglue the screw onto a little straight screw driver and start with the upper screw hole first."

This is the Kind of Battlefield short cut that you only "See" if you're in the Trenches.