Aux Coolant Pump - PeachParts Mercedes-Benz Forum

Flintster · #1 02-04-2009, 08:18 PM

The pump on my 83 CD does not work. I ran power from the battery and the pump is good. I checked the fuse and all is well. Is there a relay (or something else) I need to check?

I also changed the thermostat because I wasn't sure how long ago it had been done.

Any help would be appreciated because when MAMA's not happy neither is the rest of the world.

Any advice will be appreciated.

David

mbdoc · #2 02-05-2009, 07:58 AM

What is the problem? Low heat at idle?

That is the only job that the aux water pump does, pulls water through the heater core at idle.

The ground signal comes from pushbutton in the heating mode.

Flintster · #3 02-05-2009, 08:51 AM

Yes Low heat at idle.

What would be the best procedure to test & repair the problem? I have read of some just wiring the pump so it comes on when the ignition switch is on but, I would really not want to do that.

David

kerry · #4 02-05-2009, 09:37 AM

Many people fuse the pump with a low amperage fuse because a failure in the pump can destroy the amplifier. Perhaps someone did that with your pump and the second fuse has blown.

Graplr · #5 02-05-2009, 09:39 AM

Is your CCU in good working condition? Any other problems with your climate control system? Have you hooked up a multimeter to the pump yet? If you hook it directly to the battery it may run even though it is shot. If it is shot it could have taken out your CCU and now neither works.

Flintster · #6 02-05-2009, 09:51 AM

The only problems with the climate control is the floor vents don't have air coming out of them. My understanding this is probably a vacuum issue.

I understand a bad pump will cause other problems. I just keep thinking there is an electrical/ground (I can't even spell electrical) problem because there is no power going to the pump.

Keep them coming, I hope to spend some time on it after work this evening.

David

kerry · #7 02-05-2009, 10:26 AM

If you haven't owned it very long, look for an in-line fuse somewhere in the wiring going to the pump.

Graplr · #8 02-05-2009, 10:40 AM

Quote:

Originally Posted by Flintster

The only problems with the climate control is the floor vents don't have air coming out of them. My understanding this is probably a vacuum issue.

That also could be as simple as pressing the wrong buttons. Not all buttons open the floor vents. Read up on it in your owners manual.

If there is not inline fuse that is blown, then the problem lies somewhere along the electrical line. Hook the multimeter up the the plug for the pump and turn full heat on in the car. See if you get any voltage. If yes, then the problem is in the pump, in no, then the problem lies in the wiring or push button unit.

AMH · #9 02-05-2009, 10:41 AM

A quick test...........

Turn the key on, do not start the engine. Push the defrost button, does the pump run? Is there full heat in defrost mode? This assuming the engine is warm.

Is there voltage at the pump when in defrost mode or when the temp wheel is set to max?

The pump may be siezed and a seized pump will destroy the CCU (pushbutton unit). Do a search for my procedure adding an in-line fuse that will protect the CCU.

Also, check your monovalve for a torn diaphram. If so, replace the monovalve insert. Easy to do, just remove the insert from the top of the monovalve, four screws and it's out.

As for the floor heat, hook your Mity-Vac to the floor vacuum pod behind the center console, pump, does it hold vacuum? Does the pod open the flap when vacuum is applied?

Alan

Jeremy5848 · #10 02-05-2009, 11:35 AM

A check that you should do first is to open up the monovalve and confirm that it is in good shape. If it is partially blocked by accumulated crud or a damaged diaphragm, it could impede the flow of hot coolant, especially at idle when there is minimal pressure in the coolant circuit.

If the pump is good and there are no blown fuses (including owner-added fuses) then the problem is probably in the CCU (the pushbutton unit). As a semi-permanent bypass, you can install separate power and ground wires to the pump and connect it to any terminal that is "hot" in RUN or START (Mercedes numbers such terminals "15"). That way, the pump will run whenever the car is turned on.

If you wish to disassemble the CCU, look first for fried traces on the PC boards or other damaged components. If all seems OK, make sure all of the switch contacts are clean.

BTW, according to the FSM, the aux pump receives switched power, not ground, from the CCU. The hot wire at the pump should be black/red/violet; the ground wire should be brown. You can check the ground wire with an ohmmeter (car OFF); there should be zero resistance to engine block or chassis from the brown wire at all times. Check the black/red/violet wire with the ignition switch in position 2 (engine does not have to be running) and the bushbutton unit in "Defrost" (left-most button). You should have +12 volts and you should be able to turn it on and off by pressing buttons – ON where heat is required, OFF otherwise.

Jeremy

Graplr · #11 02-05-2009, 11:39 AM

Okay...just realized why people are telling you about the monovalve.

First thing you need to answer- Have you 100% verified the pump is not working when the car is on and the heat is on full? In my SD it is a bit hard to get to, I believe they are in easier to see locations in the CD. This could be easily done by feeling it. You should be able to tell if it is working. If you can't put the multimeter on it.

If it IS working then follow all the other intructions about why you have no heat.

Flintster · #12 02-05-2009, 02:27 PM

The pump is absolutely NOT working with the power on and the defrosters on. I turned the key on (vehicle running once and not running once) turned on the defrosters and checkeed to see if the pump was running - It was not.

I disconnected the the pump at the connector on the fenderwell. started the vehicle, put the defrosters on, and used a multimeter to check for power - NONE. I took leads from the battery and applied them to the pump and it ran, it did not sound strained or abnormal.

This just just started about a week ago. Just my luck as we are cold here now. Not critical just trying to make the vehicle right and make the little woman happier (so I can also be happier)

I do have an extra CCU from the 85 300D I parted out. I think I might give that a try before I start chasing wires. It looks like it might take only a short time to switch them out. Anything I need to know to switch them out?

Thanks for all your help so far !

David

Jeremy5848 · #13 02-05-2009, 04:35 PM

Remove two Phillips screws and then lift up and out at the top of the pushbutton unit. It's held by interlocking plastic at the bottom, lifting up clears the pushbutton unit.

With it loose, you have a string of lights and two plugs to undo, then it comes all the way out.

Flintster · #14 02-07-2009, 05:28 AM

Had the new pump and another CCU ready for the some serious troubleshooting yestderday evening. Brought the vehicle into the shop and it is working just like it should (scared of me I guess). I will keep an eye on it for the next few days to see if there are any other hiccups.

Thanks to all for your expertise. This place is great.

David

pizzachef · #15 02-07-2009, 12:31 PM

Glad its working again. Is the heat back?