Another duo valve question?

[portzy]

Are these little devices supposed to be either on or off or, do they gradually open/close as the individual temperatures reach that which is set on the dash?.

One of mine is cyclically opening and closing about once every second or so and its doing it with a very pronounced and audible, (inside the car), noise, something along the lines of a "ker-thunk", which you can also feel slightly through the steering wheel, if you can imagine that. Its only just started to make itself apparent, is this right? or just wear and tear?.

Cheers.

Portzy.

 

[Parrot of Doom]

They are analogue, and completely variable in their position.

It sounds to me like you have a fault on the heater panel in the dash. The pistons in the duovalve behave just like speaker cones in a hifi, they're extremely simple devices.

http://mbclub.co.uk/forums/showthread.php?t=26888

 

[portzy]

Hi, yes I'd seen your 'how to' but I wondered if the valves were either fully on or fully off but you have answered that for me. A dash temp selector fault eh?, do you reckon that would be stored in the diagnostics computer so they could detect what is wrong.

Portzy.

 

[Parrot of Doom]

I wouldn't have thought so although I'm no expert.

 

[Bazzle]

They open and close all the time, depends on the heat setting too. You can feel them kerchunk, kerchunk.....
Noise also comes from fuel pump pipes in their holder on firewall as pump cycles.

Bazzle