126 Duo Valve - what's with the heat...
 

A fw weeks ago I ran a thread regarding the now to be called DuoValve in my 1987/300SE Euro. After I replaced the inserts and when I still got unwanted heat I thought I might have a valve leak, which I did not. As the problem is still here and the CD is not much help with a pre 1988 Euro climate control, I write again hoping someone out there knows the Euro system and can help me.
What I now get is ample heat when I want it BUT intermittent heat when I do not call for it. I have a hunch it is something electrical in nature, but might be wrong. When calling for heat and turning the temp dial selectors to the white & red zones, I get the click sound from the valves as they engage.( there is no click when the valves disengage. Somehow gradual release feels right. Is it?)
If I turn the dial down to blue I may or may not curb the heat coming into the cabin. A possible clue comes from the dial selectors. When turning them up I sometimes hear a whiny sound that recycles - as if something is failing to connect, yet trying again and again. Almost like what a vaccum element might sound like or a potentiometer. This is a guessing game (not good) and frustrating because if mine were a fully automatic acc climate control, from reading the archives the next thing I would look into would be the Heater Core Temp Sensor. In truth, I do not even know if my car has one. I want to rule out the aux water pump, because I do get heat and there is no loss of coolant underneath either. Is this the right assumption?
hoping guidance is near...

The valves are powered with the key on and pass water unless the control ground is applied. In the "clicked" blue position the control ground should be steady. In the "clicked" max red position the control ground is removed and water flows. All other positions have the valve being pulsed with a pulsed ground signal. The pulses are large unless right at the switching temp.

Thus, unlike most heater water control valves, this valve actually control the amount of flow of water (or heat). Most valves are just open or closed.

Steve, thanks for your answer. As you often hear from members here - I too need to simplify your reply so I can better aim my energy towards solving this issue.
What is it that governs the pulsed signal sent to the valves in my particular system. The dial itself ? If so, Is the dial itself a rheostat that could be malfunctioning? I could not find anything on the CD to ouline a test to verify.

As I recall that system is described as automatic heat. The system sort of works like Klima but only automatically controls heat.

The dial assembly is the control head I think. If it were Klima the duovalves would be controlled by the PBC push button controller. I would expect the ground signals to be coming from there. Check them first at the valve.

I have the day off tomorrow and will dedicate it to the beast..
Thanks again.

update
 

Well here is what I found so far which I must admit is a little confusing.
DC volting at the valve connector and with the temp dial clicked at Blue, with koeo gives me constant ground as Steve suggested. 12.6V to be exact.
with dial clicked at red I get what I would describe as fluctuating numbers - from 4V up to 30V at one point. When clicking back to blue, we go back to constant 12.6V - I Tested both valves with the same result.
This follows the logic brought on by steve and indicates that everything is good.
Taking the car on the road however, is a different matter. The system starts properly with no heat and then provides it when requested. The problem seems to be when trying to shut it off. I click the valves to blue, yet some heat keeps coming into the cabin - with, or withour blower.
Why would the system that seems to operate correctly when stationary and cold, not work when moving and hot ?
Is it possible that I am barking up the wrong tree ? That I might actually have a problem with the flaps and they are directing engine heat to the cabin ? Or am I way off...

bump...for assistance

could be the valve itself
 

I had many happy :rolleyes: months pursuing this problem on my Euro 95 E300D.

I would suggest to start by temporarily grounding both valves under the hood so you know they have good ground. This should keep them closed when engine is warm.

If this works then you know its the ground signal from PBU that is the problem. If they still leak hot then you know its the valve itself.

In my case one side leaked hot and I eventually stumped up for a new valve :eek: -not cheap. But that sorted it. Dont buy one unless you are convinced that valve is leaking. Its an easy job to change them about 1 hour not rushing (be prepared for grazed knuckles) . I stripped my old one down to see what the problem was and it seems that coolant was leaking into the solenoids.

Hope this is useful

Keith

Hi kggkgg,

my system is a Euro non automatic climate control - therefore I have no PBU. I am afraid the valve is leaking internally - for there is no other explanation to the unwelcomed ( this time of year) presence of heat in the car.