I have an 85 300D CA version. The aux water actually works but only if I connect a wire directly to it from the battery. I get no indication of power at the point where it plugs into the wiring harness. Any ideas??

Start with the simple stuff first. Did you check the fuse in the fuse box?

Some people have installed an inline fuse on the pump to protect their CCU. Perhaps a PO did this to your car. Check the wiring on the pump as far back as you can go.

Also, how do you know it does not get power? I'm not 100% positive when it kicks on but if you turn your CCU to full heat it should be running.

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2000 E320 4Matic Wagon
1994 Chevrolet 2500 6.5 Suburban
1979 300TD

Past Mercedes
1998 E430
1984 300SD
1980 300SD

Somebody posted on here recently that it requires full heat on the temperature wheel or defrost to get the aux pump to kick in.

__________________
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
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I have exact same issue on my 84. The wheel position does not have to be on full heat for the pump to come on.

For the time being I replaced the monovalve with an L-shaped 1/2 copper pipe just to get more water into the heater core.

Haven't figured out yet what really turns the aux pump on. All fuses are ok.

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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...
96 C220
2007 Honda Accord EX
2007 Honda Accord SE V6
97 Explorer - For Sale
85 300D - For Sale
84 300D - Found Another Home
80 300TD - Found Another Home

I had assumed that the aux water pump came on by turning the ignition key into the 'on' position.

__________________
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
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Any time the CCU is "ON" (any button but OFF, the rightmost pushbutton) the aux pump should have power. [Should I be off base here, I can guarantee that in Defrost mode (far left of 5 pushbuttons) the pump will get power.]

In your [1985, ACC-III] car, the aux pump gets its power from the PBU -- that's why people add a fuse, because the pump can freeze, draw too much current, and fry the printed circuit traces in the PBU. So, one of the possible sources of your trouble is the PBU -- either a fried trace or burned contacts in a relay or switch. A blown fuse is another possible cause although that will result in more than just the aux pump not working.

A broken wire or bad connector is another possible source of trouble. If everything else seems OK, take the connector to the aux pump apart and make sure it doesn't have a broken wire at one of the two pins. Ditto the two big connectors on the PBU.

Jeremy

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"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) 201,000 miles My car
1996 E300D (W210) 289,000 miles Wife's car

"Politicians are the same all over the world;
we build bridges where there aren't any rivers."
-- Nikita S. Khrushchev

Does the Klima relay have any input to its function?? I know my fuses are OK

It does not.

The CCU controls the pump. If it's not working in certain specified modes, the CCU is almost assuredly the cause.

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Better to keep your mouth shut and be thought a fool than to open it and remove all doubt ----- Mark Twain

Thanks for the info Brian. One more question. When should the aux pump engage?

Brian, many seem to refer to the CCU also as the push button unit. Are you doing the same thing or is there another unit besides that and where is it located?

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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...
96 C220
2007 Honda Accord EX
2007 Honda Accord SE V6
97 Explorer - For Sale
85 300D - For Sale
84 300D - Found Another Home
80 300TD - Found Another Home

I did a lot of testing on this a few months ago. But, this is only on my 85. Not sure if other years are affected.

I found that the aux. pump only runs when the defrost button is depressed or if the CCU wheel is all the way to max. heat (in the detent). In any other position, the aux. pump is off.

If you think about it.... It makes sense. These are the only 2 positions that demand maximum heat (coolant flow to the heater core).

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AJ

1985 300D (SOLD)

Snookwhaler,

How did you reach this conclusion? Did you verify with anyone (i.e. MBZ tech or service dept)? I've been told that the aux pump should engage whenver the CCU is engaged. Also, I thought the aux pump forced water into the heater core when driving at low speeds or at a stop to prevent the cabin air from going cold while the wheel is heat mode (not just max heat mode).

With a meter and 3 different CCU's (engine running). It is difficult if not impossible to tell if the pump is running while the engine is on. The meter makes it possible to "see" when the thing actually comes on.

I would not trust a MB tech around here as far as I could throw them. There may be some good ones out there. But, not in Melbourne or Ft. Pierce.

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AJ

1985 300D (SOLD)

I had the same problem as you and coudn't figure out why there was no power. After much consulting of the wiring diagrams I found that the K1 relay in the CCU controls the aux pump and the footwell flaps. When you have the CCU open to resolder and check for burnt traces clean the contacts on the three relays in there.

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'82 300D - Light Ivory, 2nd Owner (Back in the wind April 2013!)

'95 E300D - White, grey interior. (Suffering from stuck/broken glow plugs)

Deuteronomy 22:4-
"Thou shalt not see thy brother's ass or his ox fall down by the way, and hide thyself from them: thou shalt surely help him to lift them up again."

just want to clarify. the CCU you are referring is the one connected to the pushbutton unit?

(Assuming what you are saying is true, i too have played with this. i replaced the CCU with a known good one and the same thing happens. Maybe the CCU attached to the PBU I am referring to is different from the CCU you are referring to?)

__________________
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...
96 C220
2007 Honda Accord EX
2007 Honda Accord SE V6
97 Explorer - For Sale
85 300D - For Sale
84 300D - Found Another Home
80 300TD - Found Another Home