I've replace the control unit twice, is that the ccu you are talking about? I'm very leery of replacing it again, especially with a new one. I may just take it into the shop. I'll explain everything so that way if it goes up again, its on them and I won't have to spend more cash on it.

As for removing the ccu, if its the one that sits behind the bottons on the center console, then its easy to remove.

Have you checked the resistance level of the wiring? Yes, the Aux water pump does draw power from the CCU, that is why many people, myself included, installed a 1 amp fuse in the power circuit of the aux wp.

That chirp sounds like a capacitor when it blows.

Have you tested the blower motor off of the battery? Have you also tested or unplugged the auw wp? Stiff motor bearings or soemthing preventing the motor from spinning will result in higher amp draw, which in turn will cause blown fuses or components.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

No I haven't tested the motor yet, I probably should be considering I suspect the motor. I was more going to test it for bearing play. Now I should test the aux water pump. Is it accessible where I don't have to remove anything to test it?

Some more info, the chirp I heard was clearly under the dash near the blower motor so that's my suspect.

How would I test the resistors? Where are they located? What values should I be looking for?

probably easier to test the auxilliary pump, particularly since it is known to cause this problem. should be easily accessible if it's anything like the 123.

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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

I believe that both the blower motor and the auxiliary water pump motor are powered through the CCU. I would test both of them before installing another CCU.

The blower motor is powered independently of the CCU.

However, the aux. water pump is a common failure and it will take out the CCU if it does not rotate. Don't ask how I know this.

If the aux. pump is not turning, it will burn the circuit board on every CCU that you put in there.

So, you must go and remove the aux. pump and test it with 12V. It's located between the two firewalls. The easiest way to get it out is to remove the section of the forward firewall to give you some room to work. If you remove the firewall section, you can have the pump out in less than 30 minutes.

Test it with 12V and ground. If it does not rotate, you've found your problem. BTW, you'll need another CCU.

I have tested the aux coolant pumps on three of my mb's and none of them are working. They wont do anything, but the ccu is functioning properly on them all. Are the mb gods smiling on me? I dont want to tempt the gods so I disconnected them for now.

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a few mb diesels

This sounds exactly like what is happening.