I have and 82 300SD. I have no blower motor. I get heat, but the blower never comes on. I replaced the control unit twice...each time it works for about 10 minutes then nothing. As soon as I switch it off or change to another button (from defrost) nothing works. I have also replaced the blower motor relay. I'm wondering if the motor is going bad (i.e. bad bushings) and is drawing too much power and somehow frying the control unit?

What else is possible? Is there another relay I don't know about? Regardless of the temp, the defrost should work right? Is there any way to test the relays?

No having a blower is getting real old.

anyone?

Are you saying it works on defrost but nothing else? Or that it only initially works on defrost and afterwards will not work at all, including defrost?

I believe I have read on this board that a failure in the auxilliary pump of some kind will cause the pump to draw too much current and burn out the board in the control unit. Some people put a fuse in the auxilliary pump circuit to stop this problem I believe. Perhaps this is your issue.

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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

This problem appears to be pretty common on high mileage D's. And it may very well be the CCU board. I received a CCU from an 83 300D the other day that I got from a salvage yard. The board is enclosed in a plastic box that looks like it can be opened up but am still trying to figure out how.

The box has slits that is probably for venting. I sprayed contact cleaner thru the slits and the cleaner residue that came out looked blackish. This tells me it gets dirty in there (after 20+ years).

I'm still trying to figure out how to open the box to get to the board. Someone said that the circuit board may develop cracks and open some circuits which then requires some soldering. Spraying contact clleaner maybe all it needs.

The other thing I am trying to figure out is how to remove the CCU from the car. I'd like to swap the units when I figure out how to remove it.

Any info would be apreciated.

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the sooner you start... the sooner you'll get done If it ain't broke, don't fix it.. Its always simpler to tell the truth...
2007 Honda Accord EX
2007 Honda Accord SE V6
96 C220
97 Explorer - Found Another Home
2000 Honda Accord V6 - Found Another Home
85 300D - Found Another Home
84 300D - Found Another Home
80 300TD - Found Another Home
Previous cars:
96 Caravan
87 Camry
84 Cressida
82 Vanagon
80 Fiesta
78 Nova
Ford Cortina
Opel Kadet
68 Kombi
Contessa

All the settings work initially for about 10 minutes. Which pump are you talking about? I was suspecting the motor was drawing too much and was wondering if it drew power through the control unit. Each time the board goes up I hear a chirping very briefly. It sounds similar to a hooter valve on a turbo (if anyone owns a Saab, you know what I'm talking about). That is why I thought it was a vacuum noise but I suppose it could have been a bushing dragging.

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.

It's the auxilliary water pump, plumbed in line with the heater hoses to push coolant thru the lines at low rpm's. I'm not sure of it's location on the SD. if you follow the heater lines under the hood, it should be visible.

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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

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.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

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.

It sounds as if you've deduced your own problem. Sometimes you can get more life out of the motor by changing just the brushes. When you pull the blower, check the armature for scoring or excessive wear. If not too bad, give the brush replacement a try. Replacements are available, along with instructions, at www.**************.com

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Sam

84 300SD 350K+ miles ( Blue Belle )

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

If the pump doesn't rotate, it usually draws too much current and fries the circuit board.

I bought an aftermarket pump and it lasted 6 months. Then, the monovalve started making some loud and steady knocking sounds.........a clear sign of problems with voltage from the pump. Unplug the pump and the problem goes away. Another example of aftermarket junk.