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  #16  
Old 05-24-2014, 03:00 PM
sixto's Avatar
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Quote:
Originally Posted by jay_bob View Post
There are 3 wires going in from the car wiring harness, and 2 going out to the motor. Note that both sides of the motor connect to the controller. Neither motor wire has a direct connection to battery or ground.
IIRC one motor wire is always 12V and the other is modulated. Low speed is something like 9V, high speed is close to 0V... just to make things interesting.

Sixto
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  #17  
Old 05-24-2014, 11:03 PM
double-dammit
 
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Quote:
Originally Posted by sixto View Post
IIRC one motor wire is always 12V and the other is modulated. Low speed is something like 9V, high speed is close to 0V... just to make things interesting.

Sixto
MB-less
OK, after reading copious amounts of low voltage instruction re. this particular system I am relatively sure that this may be beyond my scope. Should I remove the blower/fan assy to visually inspect for a possible glaring issue? It seems like the "porcupine" failure may often be symptomatic of blower failure (from what I'm reading) I can see that the brushes inside the motor are almost black. I may try removing the control unit, just to see what I can see.

I looked at the cylinder head, and was shocked to see that it's a #14. I guess it may have been repaired at some point, with 400+ K it seems unlikely it could be orig. to me from what I've read.

* Bought a Fluke (cheaper one) today at Frys…DOA but I'm sure they'll swap it out.
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  #18  
Old 05-25-2014, 04:03 AM
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Quote:
Originally Posted by beltfed72 View Post
OK, after reading copious amounts of low voltage instruction re. this particular system I am relatively sure that this may be beyond my scope. Should I remove the blower/fan assy to visually inspect for a possible glaring issue? It seems like the "porcupine" failure may often be symptomatic of blower failure (from what I'm reading) I can see that the brushes inside the motor are almost black. I may try removing the control unit, just to see what I can see.

I looked at the cylinder head, and was shocked to see that it's a #14. I guess it may have been repaired at some point, with 400+ K it seems unlikely it could be orig. to me from what I've read.

* Bought a Fluke (cheaper one) today at Frys…DOA but I'm sure they'll swap it out.
Bah! You can do it. We'll walk you though it.

What I would do:

1) Drop the lower dash cover on the passenger side
2) Unplug the wire going from the blower box to the (top left in this image)
http://3.bp.blogspot.com/-Ug6KzBWwK6w/UWCgPpvERiI/AAAAAAAACMs/E9mHFs8JErI/s1600/DSC_0039.JPG

3) There are three wires in there. Ground, 12V, Control. Probe the control wire.

4) Switch your hvac between high and low and see what your meter tells you.

If you get no change at all then its a push button unit control problem. Replace, refurbish, perform more tests on the pbu otherwise...


If you get voltage change then you've either got a blower motor problem or regulator problem.

What I would do next is drop the blower motor and regulator. Feel out the blower motor, see if it feels seized. If not..send 12V directly into the blower motor and see if it turns on..
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(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
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  #19  
Old 11-01-2016, 04:45 PM
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Ugg now my blower fan is inop as well. ( 87 300SDL ) When it works its just fine. Then - it disappears.
Some days all is good, others its MIA. Already installed a new ignition switch.
What is strange is its not just the fan, even the recirculation button is inop and I hear no actions with the vacuum switching valves and no temperature control. Just some heat creeps from the outer vents and windshield.
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  #20  
Old 11-02-2016, 10:50 AM
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Does the 87 300SDL W126 use a N29 electronic blower control unit?
If so where is it?!
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  #21  
Old 11-02-2016, 01:28 PM
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Bentrod

First check to make sure the power lead to the blower is connected tightly. I'm recalling it is the lead from the N29 regulator to the blower motor

My sdl blower became intermittent. Read as much as I could find, replaced the ignition switch, bought a new "porcupine", etc. Pulled the CCU (no joints to re-solder as in older CCUs)

After pulling the blower box cover and was starting to pull the blower power lead it "slipped" off the contact tab. So I pinched the wire lead connector to tighten the connection and bingo. Fan has now been running perfect ever since (year+) and many, many, cycles.
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Last edited by 86-300sdl; 11-02-2016 at 01:43 PM.
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  #22  
Old 11-02-2016, 01:39 PM
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Porcupine = N29 control unit

Quote:
Originally Posted by bentrod View Post
Does the 87 300SDL W126 use a N29 electronic blower control unit?
If so where is it?!
Yes...it is often referred to as the "porcupine" due to its appearance.

It is located in the blower motor box. Triangular aluminum body with lots of spines. The actual wired control unit is bolted and glued with heat transferring material to the aluminum porcupine.

Pull the passenger side underside cover, unscrew blower motor box (2 halves) assembly, drop lower half of blower box, and you'll see it.
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  #23  
Old 11-02-2016, 09:49 PM
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So on the W126 that "porcupine" is more then a simple fan resistor?
I'm loosing all control inside: No fan control, temp control, switching valve control and no recirculation light. Yet I have electrical power, and a new ignition switch.
The problem is very intermittent. When it works its all good. Or its all dead.
Pushbuttons?
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  #24  
Old 11-07-2016, 09:28 AM
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I replaced the blower fan and resistor / porcupine. Still no improvement.
On other MB models I have seen a separate " fan speed control unit " that is independent of the blower resistor.
I really need to get some heat in my car!
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  #25  
Old 11-07-2016, 10:26 AM
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The "porcupine" is not a simple fan resistor. It is basically a voltage controlled current source. The small third wire that goes into the connector is the control voltage. This is sent down by the push button unit. This voltage tells the "porcupine" just how much current to let the motor use. If I recall correctly 0V=Off, 7V= full power.

If you put a meter on the small wire, check out what voltage it is getting from the PBU. If you vary the temp and hit the high/low speed button but see no change in that control voltages then we might conclude the problem is in the PBU.
__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k
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  #26  
Old 11-07-2016, 10:32 AM
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Since you have NO reaction to anything when you're pushing buttons on the CCU, that kind of indicates that the fan is likely fine, you have a control problem somewhere. If you have power to the CCU, but it doesn't even switch the vacuum valves, you can pretty well assume the CCU is getting flaky.

The best place to start is to get a copy of the electrical troubleshooting manual and find what should be "hot" when the engine is running. If you have power at these points but the CCU isn't issuing any control signals you've found your problem.

If on the other hand, you find that you don't have power where you should, you could have a poor connection in your fusebox, a broken wire, some tab that's not making a good connection somewhere, the list goes on...

Bottom line: blindly replacing parts isn't going to fix the problem, with electrical infidelity you have to be willing to do some detective work and have the schematic handy to guide you!
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  #27  
Old 11-07-2016, 04:37 PM
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Turned out to be the push buttons!
I needed the blower fan anyhow, noisy and with 200K on it.

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