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  #1  
Old 01-14-2004, 12:36 AM
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What could cause my blower fan to kick on and off at ease?

Well it hasn't been incredibly warm (15*F) around here lately and I got the honor of driving home tonight without any heat (ok the seat heaters did work ). For the last week I haven't had much and it is really getting on my nerves (it is a bunch of things but I'd like to solve this one first). It used to mess with me a little bit so I opened up the climate control and it seemed to work flawless for a while then this came....

The climate control does a great job of managing fan speed when it is running in auto mode, the brushes on the fan appear fine (fan isn't getting any voltage), the monovalve appears to be doing its job as I don't lose heat while driving faster and it also limits my fan to a very low speed until the system is warm enough. I do hear a little extra clicking from time to time which I don't have much of an explanation for, hitting the climate control doesn't seem to help even though quite often the problem can be triggered by a earth crater in that thing with lines on it (road? or path? ). However earlier today I was stopped at a light and it decided to work and did so for the next 30mins (until I shut the car off) but next time it didn't work at all. It seems to change its mind when restarting the car however messing with the key has never got it to come back on. A few times ago it shut off the instant I turned the blinker on (hinting a ground problem?!). Are there any ways to test that coil on the passenger side fender. I'd like to know which part isn't doing its job.... Any clues or suggestions would be very appreciated.

Thanks,
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Old 01-14-2004, 08:35 AM
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Is there a good explination of just exactly *how* this ACC should function? Some things are obvious, but like the "limit fan speed to low untill engine warm" you mentioned. Mine will not turn the fan on untill there is warm air to be had, *how* warm, seems to vary with the car's mood. But if it decides theres warm air, it will kick the fan on up pretty high pretty soon. Kind of anoying.
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  #3  
Old 01-14-2004, 10:15 AM
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I believe that is under the control of the monovalve, and that isn't anywhere as annoying as not having heat the whole time!

I realized something I should add here after searching through all of the archived stuff that I also hear clicking coming from the coil on the passenger side fender (blower motor resistor?), I used to think it was the A/C compressor clutch as it is in the front of the motor but I can't feel it in the car's power so it must be the blower motor resistor. How can this part be tested?
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Mercedes W123 DIY pages are now located here.
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Old 01-14-2004, 10:19 AM
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Sure sounds a lot like the ACC control board needs to be resoldered. The solder joints for the pins will develop small cracks, cold solder joints, and then the fan begins to act up.
There are plenty of threads on that one here. You can buy a rebuilt of course, but why not DIY?
When I soldered mine I noticed there were several bad spots, they don't show without looking very closely, but they are there. I used some electical contact cleaner to clean the contacts.
So far it has worked flawlessly. Did the job last summer. Took about an hour to remove/ reinstall the unit, and about two hours to do the soldering.
I did read that there is a temp controlled Weller soldering iron available. That would be a real help for this job.
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Old 01-14-2004, 10:28 AM
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How do you get to the bottom board? I read turbodiesel had a problem like this and he had corrosion on the second board. Is the only way unsoldering the top one then removing that and then unsoldering the sides? (I'll resolder the pins as well, thanks for the suggestion) I only did the seam where the two sides and top came together before and it did help as there was a cracked solder or two. The unit is already out and the soldering iron at hand.
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Old 01-14-2004, 11:03 AM
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I never removed any of the circuit boards from the assembly. I resoldered all the pins and the seam where the boards come together, then I sprayed the contacts on those relays with electrical contact cleaner. I would not want to take that assembly apart if I absolutely did not have to. I think you would have to unsolder every pin and then try to reassemble and resolder all of those. That would be more than I have the skills to try.
I was told by a very reliable MB tech that the boards fail mostly with cracked solder joints at those pins. I got a magnifying lense out and looked at them very closely. Almost half of them had tiny cracks around the pins. I think that is where they fail.
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Old 01-14-2004, 11:08 AM
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Ok I'll give that a try, so just hold the heat on the outside of them until certain it has melted on the inside (by circuit board) then get off of it? I'll remove the side switches as well and do these pins to.
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Mercedes W123 DIY pages are now located here.
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  #8  
Old 01-14-2004, 12:29 PM
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How do you take out the ACC unit for resoldering?

Thank you

Steve
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  #9  
Old 01-14-2004, 12:46 PM
Old Deis
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I take it it is not good to overheat that board. Just hold the solder iron on them until the solder begins to flow. On a few I had to add solder, but most worked with just the heat.
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  #10  
Old 01-14-2004, 01:17 PM
Old Deis
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Like I said it takes an hour to pull that from the car. Remove the radio, the wood grained face from the center dash, it will pry off. the ash tray, and the junk box. The ACC unit has a connector and has several little black things that look like wires, but are really light tubes of some sort. Carefully pull them straight out.
That wood grained panel is the hardest thing to remove. It looks as though it will easily just break. I just kept working flat tools under it until it popped off. I have seen a few where someone has used glue to put them back on, that makes it a lot harder to get them off.
I don't recall if the ACC unit is held in with any screws or not. but it is not that hard to get it out. About the same size as the radio.
Good time to replace the small lights there while it is out.
Reinstall is about the reverse of taking it out.
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Old 01-14-2004, 01:32 PM
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I have a page on my site about removing it. On the 126s you have to pull the radio, the 123s don't. Sometmes there are two screws at the top other times there aren't. My wood panel was glued before to.
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Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k
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  #12  
Old 01-14-2004, 02:49 PM
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Might be as simple as the brushes on the fan motor. A quick $6.00 fix. Worth checking out.

Joe.
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