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#1
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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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#2
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Check your relays.
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1983 Mercedes-Benz 240D Automatic, A/C, Power Sunroof, Power Right Side Mirror 231K Miles FOR SALE MAKE OFFER |
#3
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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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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground. 1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers. 1986 Mercedes-Benz 300D - Sold, Euro non-turbo car. |
#4
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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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Sam 84 300SD 350K+ miles ( Blue Belle ) |
#5
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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
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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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#7
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Quote:
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83 SD 84 CD |
#8
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Try resoldering the CCU.
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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver 1982 300SD - 232K miles - Wife's Daily Driver 1986 560SL - Wife's red speed machine |
#9
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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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Sam 84 300SD 350K+ miles ( Blue Belle ) Last edited by SD Blue; 06-04-2008 at 10:38 PM. |
#10
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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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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#11
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#12
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#13
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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. |
#14
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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
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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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Sam 84 300SD 350K+ miles ( Blue Belle ) |
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