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  #1  
Old 01-13-2010, 02:24 PM
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Aux Water Pump Inop; No Power at Plug

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??

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  #2  
Old 01-13-2010, 02:34 PM
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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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  #3  
Old 01-13-2010, 02:57 PM
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Somebody posted on here recently that it requires full heat on the temperature wheel or defrost to get the aux pump to kick in.
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  #4  
Old 01-13-2010, 04:06 PM
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Quote:
Originally Posted by kerry View Post
Somebody posted on here recently that it requires full heat on the temperature wheel or defrost to get the aux pump to kick in.
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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  #5  
Old 01-13-2010, 04:09 PM
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I had assumed that the aux water pump came on by turning the ignition key into the 'on' position.
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1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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  #6  
Old 01-13-2010, 04:54 PM
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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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  #7  
Old 01-13-2010, 07:30 PM
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Does the Klima relay have any input to its function?? I know my fuses are OK
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  #8  
Old 01-13-2010, 11:40 PM
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Quote:
Originally Posted by diesel85 View Post
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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  #9  
Old 01-14-2010, 01:21 AM
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Thanks for the info Brian. One more question. When should the aux pump engage?
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  #10  
Old 01-14-2010, 08:11 AM
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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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  #11  
Old 01-14-2010, 10:40 AM
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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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Old 01-14-2010, 02:32 PM
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Quote:
Originally Posted by snookwhaler View Post
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).

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).
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  #13  
Old 01-14-2010, 03:18 PM
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Quote:
Originally Posted by diesel85 View Post
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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  #14  
Old 01-15-2010, 12:05 PM
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Clean the K1 Relay

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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  #15  
Old 01-15-2010, 04:16 PM
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Quote:
Originally Posted by fdanielson View Post
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.

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?)

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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
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97 Explorer - Found Another Home
2000 Honda Accord V6 - Found Another Home
85 300D - Found Another Home
84 300D - Found Another Home
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