[mikedewilk]

I am sometimes not getting heat into the cab and am told it is the Duo Valve. Touble is, I don't know where it is or what it looks like !!! I am running an E270 classic diesel estate.

Any suggestions ?

Mie.

 

[Diesel Benz]

I am sometimes not getting heat into the cab and am told it is the Duo Valve. Touble is, I don't know where it is or what it looks like !!! I am running an E270 classic diesel estate.

Any suggestions ?

Mie.

Is it a W211? If yes, it does not have a duo-valve but a heat exchanger shut-off motor.

Model specific forum would have better info. An example here:
DIY: Installing a new Changeover/Heater Control Valve - MBWorld.org Forums