All heat all the time, mono valve/aux pump - PeachParts Mercedes-Benz Forum

renaissanceman · #1 03-21-2015, 08:51 PM

W124 1987 300D, with Automatic CC.

I had thought I had identified the mono valve (or heater valve?) near the battery before, as seen in the center of the photos below:

I think this may be the wrong part, as it doesn't look any thing like the diagram in the W124 FSM?

I think I was mistaken before when I thought my aux pump was not working, because when the engine is hot, I can get smoking hot heat out of the vents for many minutes, and I can watch the temperature gauge slowly drop. This makes me think the circulating pump is working.

The part in the first photos makes a humming noise when the heat is on, like I would expect a pump to sound. Have I found the auxiliary coolant pump?

Where is the mono/heater valve? It's warming up here, and having to keep the CCU in the off position with heat still seeping out is getting old. I'd like to diagnose and correct the problem ASAP (I'm planning to take the car to California in two weeks).

Thanks again!

renaissanceman · #2 03-21-2015, 09:02 PM

Looking at the pelican listing for the aux pump, the pictured unit appears to indeed be the pump. So half the mystery is solved -- now I just need to find the heater valve.

rob300SD · #3 03-21-2015, 10:17 PM

Should be nearby that pump likely connected to it by a short hose.

renaissanceman · #4 03-21-2015, 11:00 PM

I guess I'll have to pull the battery and have a closer look...it's not immediately apparent.

I've heard that the aux pumps should be fused with a 1A fuse to protect the CCU in case of motor failure?

BenzTurbo · #5 03-21-2015, 11:15 PM

i don't think that pump should be there. that's where the monovalve goes. it isn't even secured. aux pump should be on the driver's side of the heater connections. at least on the diesels...

renaissanceman · #6 03-21-2015, 11:44 PM

Hmm. Well the pump appears to be (nearly) brand new and is just zip tied to the brake line...maybe the PO's mechanic made a mistake and put the new pump in the place of the mono valve...

...which would explain the incessant heat!

Where is the pump supposed to be? Under the washer fluid reservoir? If someone with an 1987 with a 603 would verify the monovalve/pump location, I'd be very appreciative.

Jeremy5848 · #7 03-21-2015, 11:56 PM

The aux pump does not need to be fused in the 124 as the PBU is internally current limited and shuts off if there is an overcurrent due to a short circuit or other failure. The 123 PBU does not have this protection; when I had one I fused the aux pump.

As to the item in the picture, that is indeed an aux pump; the monovalve should be mounted there—it was there next the battery when I had an '87 300D Turbo. Without a monovalve you will have heat all the time. The aux pump should be located on the right side of the engine bay not far from the turbocharger, in the coolant line between the thermostat housing and the monovalve.

Jeremy

BenzTurbo · #8 03-22-2015, 12:14 AM

w124 603 diesel has the aux pump under washer tank and monovalve in front of battery. there is nothing to control hot coolant flow.

renaissanceman · #9 03-22-2015, 12:25 AM

So I guess I've got a monovalve order from Pelican in my future. I think I have two aux pumps on this thing, and one pumps when the CCU commands shutdown of the monovalve.

Le Sigh, previous owners and their MB ignorant mechanics.

renaissanceman · #10 03-22-2015, 08:27 PM

I have a valve on order from Pelican. It looks like the mounting tabs are still on my car, but the little rubber pegs that the valve slips onto are gone. Looks like I'll be designing and 3D printing some plastic replacements.

The electrical connection is also not a plug similar to the others on the vehicle (like I'm assuming it should be), but is two independent wires with some type of factory-looking barrel connectors on them. I'm wondering if they got de-pinned from a connector by whoever bastardized my heater system.

Solenoids are typically non-polar, so I'm thinking I'll put them on however I see best fit unless I can figure out which is which and the pins are marked on the new valve. One line should be +12v at all times, while the other is ground triggered by the CCU, correct?

rob300SD · #11 03-22-2015, 08:34 PM

No idea. I guess either it will work or it won't sounds like you'll figure it out once the part shows up. Hope it works out!

BillGrissom · #12 03-22-2015, 09:50 PM

As many have, I replaced the electric "aux pump" in both my 300D's with a section of 5/8" heater hose. I used silicone since easier to fit the different sized ends. Heat still works fine. I don't live in frigid Germany.

renaissanceman · #13 03-22-2015, 11:37 PM

Well, as I have an essentially brand new one courtesy of the PO, I'll put it in and run it until it fails.

Isn't it made for cooling hot spots in the head more than CC use? I really like having heat with the engine off, anyway.

Jeremy5848 · #14 03-23-2015, 11:14 AM

The aux pump was added, so the stories told us by our grandmothers go, because people in cold climates complained of insufficient cabin heat in slow city traffic. At slow/idle engine speeds, the main water pump doesn't move enough hot coolant through the heater core so the aux pump was added.

OTOH, the aux pump does indeed move coolant through the head more efficiently, helping keep it at an even temperature, but only when the monovalve is open, so that is probably not the primary reason for the pump. In the OM606NA engine used in the 1995 E300D, however, there is a loop that bypasses the heater, allowing coolant to flow through the head via the aux pump whether the heat is "on" in the cabin or not. That mod was used almost certainly as an anti-smog device and appears to be unique in that model-year-engine.

Jeremy

renaissanceman · #15 03-26-2015, 10:57 PM

So I got the heater valve in, and it on and off when the climate control is active. I'll take her for a drive tomorrow to see how it actually regulates temperature. Now I need to get in and replace the aux pump. I need to figure out how the windshield tank comes out to gain access.

I'm going to have to design up some pegs to constrain it, however...It's currently floating above the mounting points.