W124 Duovalve query

[doshbass]

Dear Forum,

I had the typical 124 problem of an always hot heater. This wonderful forum pointed me in the direction of the duovalve and associated fuse.

In my case it was corroded connections on the wiring to the duovalve and after a quick cleanup I now have hot and cold on both sides - ****** marvelous.

Now the query....

I first went to check the fuse using a 12 volt light up type tester. I checked the top and bottom and found power at both ends, however when I took out the fuse, I still had power at both ends. This strikes me as odd.

Could there be any scenario when this should happen, or does it look like a wiring bodge somewhere?

 

[television]

Dear Forum,

I had the typical 124 problem of an always hot heater. This wonderful forum pointed me in the direction of the duovalve and associated fuse.

In my case it was corroded connections on the wiring to the duovalve and after a quick cleanup I now have hot and cold on both sides - ****** marvelous.

Now the query....

I first went to check the fuse using a 12 volt light up type tester. I checked the top and bottom and found power at both ends, however when I took out the fuse, I still had power at both ends. This strikes me as odd.

Could there be any scenario when this should happen, or does it look like a wiring bodge somewhere?

I cant comment exactly for your case,the reason could be that there is a lamp or some thing that is normally grounded when running ,but just floating as we call it. very hard to explain. Another example is say a rear light with a ground problem, you will get a reading on both connections of the bulb,take the bulb out,and the voltage goes. A reversing lamp will have 12v on both terminals if the reverse switch is in the ground lead.

Hope it helps a little. Malcolm

 

[doshbass]

I guess I'll work on the principle of "if it ain't broke" but is anyone feels like testing their fuse number 7 to see if they have the same thing, it would be interesting to know.

Jon

 

[42731]

300ce-24v

Just a thought but the water pump on my car corred on the inside - vanes, I think, and the temperature rose quite high.

 

[Bolide]

I believe a Duovalve is just a solenoid acting as a water valve and it works not by opening a certain amount, proportional to an applied voltage as you might expect, but by having a pulsed DC voltage applied. The temperature is set by the duty cycle (ie relative duration of +ve and -ve) of the pulsed DC. If you got the duty cycle just right I assume you could hold the solenoid partially open against a return spring. You might need a scope to see the control voltage swing as a DVM won't react fast enough. That's my theory, anyway

As Malcolm says, it may be the type of device where you put +12 volt either side of it to stop it working then drop one side to earth to start it

This is the kind of devious stuff MB engineers dreamt up before everything was digitally controlled

Nick Froome
www.w124.co.uk

 

[doshbass]

Sounds confusing to me. What I saw was 12v on the centre PIN, then a switched -ve on each of the other two pins depending on switch position. I will probably have a look to see what happens with the switch in the half open position.

Either I will get resistance or if it as you say, my meter will have a fit.

Whilst on the subject however, I have lots of niggling problems with the big round pin type plugs. I have tried wet and dry and some wd40, but I inevitably get problems. This particular problem re-occurs and I need to fiddle the connections and have the same problem with the O/S headlight connector.

From peoples experience is this a socket to pin problem or perhaps a wire to socket problem, and has anyone found the correct way to stop it happening.

Jon