Trying to locate the aux water pump to the heater core on a 1992 400E. My heater stoped working and I suspect this part may be at fault or was left dissconnected after my recent valave job.

Have attached a very part pic, it hopes that someone could help me locate its location. Hopefully its accessible and does not require the removal of any major parts like intake manifold or the radiator.

Thanks

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I do not have a digital camera, otherwise I would post the picture. It is easy, locate the ECU box, passenger side behind the engine firewall. The Aux water pump is in front of the ECU box (front is toward the front of the car) it is installed vertically, tubing connections on the bottom. Or snap a picture of the ECU box area and I will circle it for you.

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2010 ML350 Bluetec
2012 Mustang Convertible

Thanks, I think I loacted it, I took a pic and circled it in red. Is this the aux water pump?

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Yup, that's it!

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

It's unlikely that the problem is your aux water pump. The purpose of that pump is to circulate hot coolant to the heater core when the engine is idling (e.g., when stopped at an intersection). If you're not getting heat at all, there would have to be another problem in the climate control system. The monovalve could be at fault, although the more typical fault mode for that part is to go into full heat mode. Might want to search on "monovalve" and see what turns up.

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Steve
'93 400E

Would the mono valve be part 56 on the diagram? and is it located behind the ECU?

It appears that you are correct.

I've attached a picture....yours should look alot like it.

See the 4 screws? If you remove them, the valve itself will come out, along with a part or two. Just be sure an note which goes where. Might want to make sure your connections are good first, before you take stuff apart. Everynow and then, you get lucky, and its just a groady connection.

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__________________
It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

Thanks for the picture. Since the monovalve defaults to open if it has failed and the aux water pump just circulates the coolant, then whats next?

Climate control unit? The AC works great I get a really stronge flow of cold air, so I know part of the climate control unit works.

My symtoms are: if I turn on the heater to full, I get warm air for about 20 seconds, then it turns to regular. I think this may be warm air that is just trapped in the system, because it only does this after the heater has been stated once. If you turn it off then back on agian you get just regular non warm air..

I do get some slight condensation around the windows after engaging the heater as well. I guess since I should never be getting condensation perhaps the heater core has developed somekind of leak?

If you're getting significant condensation but NOT smelling the usually very obvious smell of engine coolant, seems to me that there would most likely be a problem with the recirculation flap (so that you are just recirculating cabin air instead of bringing in outside air). If your heater core was leaking to the point of causing water vapor to condense inside the car, you would HAVE to smell coolant.

I have read that monovalves DO fail in the closed condition. Monovalve failure is so common that you can get a repair kit (to replace the rubber diaphragm inside the monovalve) instead of having to replace the whole thing. I am far from a climate control expert, but from what I've read over the years, it's a cheap, simple fix so might be worth starting there.

The other possibility, which you voiced in your first post, is that a vacuum line got disconnected under the hood. I know that when my evaporator was replaced, that happened. However, the system is designed to default into full heat/full defrost mode so this may be less likely.

The CD-ROMs have a nice, if tedious, procedure for testing the climate control system and locating faults.

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Steve
'93 400E

I think I am going to start with the monovalve. A new monovalve is about $100, so I'm look for that repair kit (to replace the rubber diaphragm inside the monovalve). I tried the local MB dealer, but they do not carry such a kit. Could someone please direct me to a place that might?

Thanks