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  #1  
Old 06-04-2008, 11:54 AM
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'82 300SD Blower Motor (bench test OK, but non-functional in vehicle)

Per Brian Carlton's recommendation, I applied 12V directly to the blower motor in my 300SD. The motor runs. However, when it's connected to the vehicle wiring, I cannot get it to activate. I've tried every possible combination of climate control settings (including defrost) but to no avail. I checked the blower motor fuse in the main fuse box on the driver's side of the engine bay, and it is intact. (To rule out a hairline fracture, I substituted a piece of copper wire. Still no luck.) Where should I turn my attention now?

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Old 06-04-2008, 11:54 AM
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Check your relays.
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Old 06-04-2008, 12:17 PM
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Have you verified that there are 12V coming out of the vehicle connector at the blower motor when you turn it on?
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  #4  
Old 06-04-2008, 12:27 PM
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On your car, F11 powers the Blower Motor Controller and F10 powers the Pushbutton Controller. Also, did you try the fan mode in High rather than Auto?

If these don't produce anything, then the problem may be broken solder joints in the Pushbutton Controller. The circuit boards are arranged in an "H" pattern and the solder joints, where they meet, are prone to cracks. Resoldering may be needed. Do a search for "resoldering" and "pics" or "photos" for more details. Not a difficult job but if your not comfortable with a soldering iron find a buddy who is and he can have it fixed in less than an hour.
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Old 06-04-2008, 12:51 PM
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Quote:
Originally Posted by TTCummins View Post
Have you verified that there are 12V coming out of the vehicle connector at the blower motor when you turn it on?
Good idea... I just went down and verified that there are 0.00V at the vehicle connector at all times (no matter which buttons I press on the climate control panel.) I will check the relays next, as the post above suggests.
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  #6  
Old 06-04-2008, 12:53 PM
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I'm also reading more and more about some "evil servo" in this type of car. If it's going to be a huge hassle just to get the blower motor to operate, then I'll probably just steal 12V from somewhere and installed a manual switch. I just need some air flow in the cabin on warm days.
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Old 06-04-2008, 02:24 PM
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Quote:
Originally Posted by jtocwru View Post
I'm also reading more and more about some "evil servo" in this type of car. If it's going to be a huge hassle just to get the blower motor to operate, then I'll probably just steal 12V from somewhere and installed a manual switch. I just need some air flow in the cabin on warm days.
I think an '82 does not have the "dreaded servo" you're referring to. The CCU in my SD has started to not function properly, I'll check those relays, how do I know if they are not any good?
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Old 06-04-2008, 03:09 PM
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Try resoldering the CCU.
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  #9  
Old 06-04-2008, 10:32 PM
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I have hashed and rehashed a climate control system identical to yours.............and let me say I don't know what relays would be involved with the blower motor.

Your system........

Fuse........Pushbutton Controller
to
Fuse........Blower Motor Speed Controller
to
Blower Motor

In order of likelyhood from what you described: Fuses F10 & F11, ACC Pushbutton Controller

Note: Ensure there is actually 12VDC at both sides of those fuses as someone, in another post, mentioned an ignition switch problem where several fuses had intermittent power.
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Last edited by SD Blue; 06-04-2008 at 10:38 PM.
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  #10  
Old 06-05-2008, 01:58 AM
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Another possibility

Does the 300SD use the same or a similar set of resistors (to adjust the fan speed) as my '85 300D? The resistors (look like coils of wire) live in a metal box, usually sits on one of the inner fenders. If the right contact broke in that box, no current would flow to run the fan; no voltage would be measured at the fan terminals.

Even so, my first guess would be fuses and then the push-button "CCU" controller.

Jeremy
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  #11  
Old 06-05-2008, 11:36 AM
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Quote:
Originally Posted by SD Blue View Post
In order of likelyhood from what you described: Fuses F10 & F11, ACC Pushbutton Controller

Note: Ensure there is actually 12VDC at both sides of those fuses as someone, in another post, mentioned an ignition switch problem where several fuses had intermittent power.
Verified that I have 12V on either side of fuses 10 and 11 when the defrost button is pushed and fan setting is on "high." When I push the clear, right-most (i.e., "off") button on the pushbutton controller, I have 0V at those fuses. So, I'm confused.. it seems like the pushbutton controller isn't entirely broken, if it's switching power correctly. I guess that means it must be the part of the controller that sends power to the blower...
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  #12  
Old 06-05-2008, 11:38 AM
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Quote:
Originally Posted by Jeremy5848 View Post
Does the 300SD use the same or a similar set of resistors (to adjust the fan speed) as my '85 300D? The resistors (look like coils of wire) live in a metal box, usually sits on one of the inner fenders. If the right contact broke in that box, no current would flow to run the fan; no voltage would be measured at the fan terminals.

Even so, my first guess would be fuses and then the push-button "CCU" controller.

Jeremy
I do have that "swiss cheese box" underneath the brake booster. It's completely covered with leaves and pine needles, so I wouldn't be surprised if something is fried down there. Getting access to that ought to be fun...
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  #13  
Old 06-05-2008, 08:51 PM
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Quote:
Originally Posted by jtocwru View Post
Verified that I have 12V on either side of fuses 10 and 11 when the defrost button is pushed and fan setting is on "high." When I push the clear, right-most (i.e., "off") button on the pushbutton controller, I have 0V at those fuses. So, I'm confused.. it seems like the pushbutton controller isn't entirely broken, if it's switching power correctly. I guess that means it must be the part of the controller that sends power to the blower...
Once you've confirmed that you've got the blower to operate, the problem lies in one of three places:

1) CCU (most likely)
2) Blower controller (possibility)
3) Resistors (least likely).

I had the identical problem and could not figure out a good way to isolate the issue to one of the above three. I swapped another CCU into place and the problem was solved.

If I were you..........I'd go with a CCU swap and see how you make out. If not, then the next step is the blower controller.
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  #14  
Old 06-05-2008, 09:42 PM
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I had the same problem and the traces on the CCU board were burnt up. This is usually caused by the Aux. water pump being locked up in the inside fire wall beneath the battery. Fix the traces with wire or resolder and unhook the water pump plug right next to it and see if it will not work then. I found out the hard way and burnt up TWO CCU before I found out the pump goes trough the CCU. When the pump is fine the board will pull less than 1 amp. When the pump locks up you have smoked the CCU. If the pump is bad replace it and put a 1 amp in line fuse with it and no more fried CCU. Good luck!!!
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  #15  
Old 06-06-2008, 10:54 AM
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Quote:
Originally Posted by jtocwru View Post
I do have that "swiss cheese box" underneath the brake booster. It's completely covered with leaves and pine needles, so I wouldn't be surprised if something is fried down there. Getting access to that ought to be fun...
As Brian mentioned, blower motor resistors are very unlikely, unless you see some burnt material in the area. BTW, a note of precaution, you need to keep that area clear of debris (I know it's a never ending task and I'm as guilty of letting go too long). If you do a search of "W126" and "fire" you might even find photos of what I'm talking about.

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