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#1
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Blower blues
In the past, when the AC blower wouldn't come on, I used to be able to jump start it by pressing the defrost button. Now that no longer works. The following have been tested and shown to be in working order:
Blower fuse Blower Blower regulator I'm assuming CCU is working because I can hear the compressor click when pressing the buttons Any ideas?
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'83 SD, 2x '85 SD You are entitled to your own opinions, you are not entitled to your own facts. |
#2
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Quote:
If this does not work, and I suspect that it will not work, get a rebuilt CCU. |
#3
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I'd also suspect the brushes. The increased voltage in the defrost position may be overcoming the poor connection. There are threads on here describing how to replace the brushes.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#4
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blower blues redux
I ended up not looking into the CCU (as recommended by B Carlton) at the time I started this thread because the blower came back on and this was the CCU that I had resoldered shortly after purchase of the car 4 years ago curing all the problems (blower was then not an issue) I had with it back then. While it worked, I unplugged the temp switch sensor (I assume its the plug located on top of the thermostat housing where radiator hose attaches) which did not stop blower function.
The history since my original post is that on one occasion I was able to revive it by replacing the melted fuse (#11). From then on it has worked for months, stops working for weeks, comes back on for 20 minutes, quits again. No correlation to going over bumps or anything else. Before ripping the CCU out again, does this sound like CCU symptoms? If so, what part of the CCU governs blower function?
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'83 SD, 2x '85 SD You are entitled to your own opinions, you are not entitled to your own facts. |
#5
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I would recommend checking the blower motor. The symptoms in your first post sound very much like the problem I had with my '85 300D some years ago. The brushes and the commutator were badly worn; I ended up replacing the motor. I don't know how similar is the 300SD (or not) but the blower is the first item I would check.
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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 |
#6
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I understand short brushes will melt fuses as it will draw more amperage.
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83 SD 84 CD |
#7
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As stated in my original 12-26-2009 post, the '83's blower had been tested good -swapped it with the known good from the '85. Result: '83's blower worked fine in the '85. '85's known good blower did not work in the '83.
Now you ask: why not ""simply""swap CCU's? Because that whole radio/ashtray/surrounding buttons CCU panel is an infernal rats nest of bad design, flimsy manufacture, brittle snap/push/bend/twist in removal and reinstall which never goes back in as it should and won't improve with repeated removal. I had done both cars, cured all AC issues ended up with both radio face plated not engaging solidly. So I don't want to go back in there unless all else exhausted. And then only pull the suspect '83 CCU and fix it, for which it would be nice to know which area governs blower function.
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'83 SD, 2x '85 SD You are entitled to your own opinions, you are not entitled to your own facts. |
#8
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Define "tested good." The 126 blower is mounted vertically which loads the bearings in a way not conducive to an infinite life. The blower can test positively while on its side or even vertically in a static environment. Add the vertical jarring of driving the car and it's possible the brushes shift enough because of bearing play to lose contact.
Sixto 87 300D |
#9
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Testing blower as mentioned in my penultimate post involved exchanging blowers (fully installed in normal operating position) between my '83 SD (the car we are troubleshooting in which the blower was not working at the time of test) and the '85 SD whose AC is fine.
Result: '83's blower worked fine in the '85. '85's blower did not work in the '83. Conclusion: blower is not the problem.
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'83 SD, 2x '85 SD You are entitled to your own opinions, you are not entitled to your own facts. |
#10
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Oops, I missed that. Carry on
Sixto 87 300D |
#11
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blower issue resolved
Brian Carlton's diagnosis got it right: The CCU was bad.
__________________
'83 SD, 2x '85 SD You are entitled to your own opinions, you are not entitled to your own facts. |
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