any way to test aux wtaer pump function? - PeachParts Mercedes-Benz Forum

mike riemann · #1 12-17-2002, 11:09 PM

I'm just about to buy a replacement aux water pump to cure a nonfucntioning heater (bypassing the mono valve does not increase water flow to the core). Any way to verify the aux pup function just to be sure it is not functioning?

rwthomas1 · #2 12-18-2002, 12:03 AM

I was under the impression that the electric pump only assisted water flow at low rpm? It would be fairly simple to remove it, put some hose on it, hot-wire it and test it. It should be fairly obvious if it doesn't work. Should also be an easy boneyard score? RT

mike riemann · #3 12-18-2002, 08:22 AM

RW,
Thanks for the note...I get NO significant heat when driving around or just idling...just a short puff of warm air, then the discharge air goes cold...the blowers work fine...I have bypassed the mono valve in a effort to isolate the problem, but that had no effect on the problem. I was thinking that perhaps the aux pump was inoperative and thus impeding water flow...maybe I'll bypass that too just to see if it has an effect...I just don't want to slap a $130 part in if that is not the real problem...

#4 12-18-2002, 08:48 AM

There is test in archives.
But here goes.
There are two wire going to pump to supply voltage. One is a nutral or ground and one is the positive lead. I beleive that the black wire is ground. This can be checked with continuty tester.
Then take a wire with clips on it and connect it to positive and connect other end to Pos. of battery. You will eather hear it running or feel it running. It it does run pumps bad.
In archives there are articles about cutting the positive wire and inserting a 1 amp slow blow glass fuse and holder to protect the Climate control unit from burning out. Climate Control
unit is $300 to replace. The fuse and holder may be $5.00. To me that is cheap insurance.
The above test is done on the car with all plumbing attached.
Good luck.

jcd · #5 12-18-2002, 09:19 AM

Not sure if the aux pump is your problem. I "think" You should get enough positive flow thru the system when the engine is at high RPM. Last year I had a bad servo, my 1977 does not have the mono valve, and I would only get heat when the engine was at high RPM's. My aux pump worked when hot wired, but it did not work when the heat was on, conventional wisdom is that it is an issue with the push button control unit. I would guess that is your problem, not the pump.

JCD

P.E.Haiges · #6 12-18-2002, 09:27 AM

If the pump runs when "hot wired" as Charlie suggested, try driving the car with the pump "hot wired"and see if that makes any difference. If you now get heat, the pump may not be turned on when it should be and you will have to find out why.

P E H

mike riemann · #7 12-22-2002, 08:47 PM

thanks to all for your info and opinions...the saga continues....OK so I have now removed the aux pump, hot wired it and it does turn very nicely...just for fun I also bypassed the aux pump to see if I get heat while driving at highway speeds...no change in behavior...hmmmm...I will NOW hot wire the aux pump to run all the time (temporarily of course) and get the thing up to operating temperature...if there is heat, I will deduce that the climate control sw is not signaling the pump to come on...and/or open the mono valve...more later...

Motorhead · #8 12-23-2002, 12:53 AM

I would replace the capsule in the mono valve. That sounds like the problem to me. My wifes '84 TDT did the same thing and it was the valve capsule. It is a very easy repair. Also, do the lines to the mono valve get hot when engine is running? You should also ck the tube to make sure it is not clogged from the water pump to the valve. Ck the outlet at the water pump, it can clog also. Ck that you have flow thru the heater core. take the hoses off and run a water hose,at low pressure, thru it to see if it is clogged. Ck voltage at the mono valve with a test light. It will glow dim if it has juice to it I'd bet on the mono valve being faulty.
Chris

jerryb · #9 12-23-2002, 02:58 PM

Forget the aux water pump, just leave it bypassed, the mono valve is like a solinoid, if the rubber is ok and the valve moves when clicked on it's ok, default is full heat anyway so I doubt that's the problem. They do air lock very easy and are hard to burp, you might pull the upper hose off the rad. and fill with coolant, if that doesn't work you will have to find a way to force coolant through the the system to find the blockage.

lrg · #10 12-23-2002, 11:44 PM

I disagree on the "default" mode of the monovalve. Mine had a small tear in the rubber and I got very little heat. I replaced the center core and then I got all the heat I could want. I my case the default was not enough heat, not too much heat. If you bypassed the monovalve by connecting the two hoses around it you can probably eliminate it as a cause. If you "bypassed" it by opening the valve with a direct wiring then you still haven't ruled the monovalve out as a potential source of your problem. The aux pump is really only supposed to be necessary at lower RPM (but if you like heat in stop and go traffic it's a worthwhile assist). If you are not getting heat at highway speed it's more likely the monovalve or CCU.

mike riemann · #11 12-24-2002, 08:45 AM

Thanks for the follow-up opinions...let me be more specific on my current situation. 1) bypassed mono-valve means I removed it had cross connected the hoses from the tubes...i.e. no valve in the water circuit 2) by passes aux pump means the same..I have it in the trunk and a direct connection where it used to be. Still when th motor reaches operating temp, an I turn on the blower (which works fine)I get about 15 seconds of warm air, which cools rapidly to brrrr. I was thinking core blackage, so I was getting ready to try a gentle push (water) from the garden hose into the core tube...I also have a really big hammer, but was saving that in case the more rational remedies fail. More opinions welcome!

jerryb · #12 12-24-2002, 11:54 AM

I still think you may have air in the system, after all you have done that or blockage is all thats left, and blockage is unlikely but air is likely after all the times you have opened the system.
They don't always self bleed and I have had them be very dificult after a flush and drain.

MVK · #13 12-25-2002, 10:38 PM

I have discovered a very easy way of testing this pump without removing it or any coolant lines attached to it.

Considering that this pump is wired properly and all connections are fine, fuse ok etc etc. do the following

At the end of the motor, you will see a black plastic protective cap, gently pry it out with a screw driver( dont loose the cap). Now you will see a steel center which is the shaft of the motor.

Now turn on the engine, and engage the temp setting to full hot, and press the defrost button. This by default must and I say it again MUST kick in the aux water pump.

Now go to the pump, and put your finger to the center of the shaft and feel for the rotating shaft. If you feel that the shaft is turning, the aux pump motor is fine. If its not turning, tru gently tapping on the electric motor(not plastic pump) body all around, sometimes, the worn out brushes do make a contact this way and may last you for few months or more.

ALSO LOOK FOR MY PREVIOUS POSTS FOR REPAIR OF THIS PUMP WHICH IS A LONG SHOT BUT MAY WORK. MINE IS STILL WORKING AFTER A MINOR REPAIR.
Do a search under my name mvk and keywords watre recirculating pump repair.

I rebuilt my auxiliary water pump

Hope this helps

MVK