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Old 11-14-2002, 06:34 PM
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Join Date: Dec 2001
Location: Fairfax, VA
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W124 300D 2.5 *Wierd* ACC Problems

Hopefully somebody out there can help, I think this thing is possessed...

Issue 1 - Temperature fluctuates with idle. I had the dial in the red area for heat, but the temperature kept changing depending on idle speed of the engine.. Vacuum issue? Bad control unit??

Issue 2 - On the control unit, after driving for some time, the lights dimmed out. I stopped the car, shut off the motor, turned off the lights. I turned the lights back on very soon after, and the panel lit - dimly. The longer I waited, the brighter it got, but each time it faded back out. I went in the store for about 5 minutes, came back out, lights on - it fas fully bright again, and stayed that way for the rest of the 5 minuted drive home... ???????? Again, bad control unit?

Thanks for the input -

-Reed

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Old 11-14-2002, 09:32 PM
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Join Date: Aug 2001
Location: Milford, DE
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1- At idle there is not enough coolant flow for reliable heater operation. There is a aux water pump in the cooling circut that is supposed to help with this problem but it does not seem to work all the time. I think you will find that the heater does not work too well when you are idling for an extended period. When you accelerate there is now plenty of coolant flow thru the heater core so you get a big blast of hot air until the climate control circut re-adjusts to the new flow rate.

2- I think the lighting for the ACC buttons are simply small 4w lights driven from the instrument panel illumination circuts. Are the dash lights varying in intensity? I don't think flickering lights in the ACC unit indicate a bad ACC unit - the lighting is independent of the internal components.

Tim
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Old 11-15-2002, 08:34 AM
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Location: Fairfax, VA
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Thanks for the info on coolant flow. Hadn't heard that before. I wonder if the auxiliary pump could be malfunctioning...?

On the lights - this is what seems wierd to me - the rest of the dash lights were fine. Just the ACC panel dimmed, and eventually went black - then came back to varying degrees depending on how long I turned it off for... ???? This morning I had my lights on the whole way to work, and while it was lighter outside and not that easy to tell how bright the lighting was, it did appear to be on...

-Reed
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Old 12-29-2007, 10:37 PM
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Join Date: Apr 2007
Location: Maryland
Posts: 83
CCU lights come on then go out?

Thought I would resurrect this thread as i am having a simlar problem with my 87 190D, and found no solutions in my search.

My CCU lights were out, so I replaced the bulbs, they worked for about a half an hour and went out. Then, later that that same night when I restarted the car, they came back on again for a while and then went out. All the rest of the dash lights work fine. . . . it is a mystery to me

Thanks for any help
George

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