[Mercefreaken]

My parents have a ´99 W220 S320 with the 4-zone air conditioning.
The problem is that they only get hot air from the rear vents, no matter what they do. Several workshops - including the MB dealer and another workshop that were supposed to be experts on air conditioning systems - have looked at it, but they just replace parts in the hope that they´ll get it right sooner or later...

Are there separate duo valves for the rear air con? They have allready replaced some kind of valve placed in the rear (I wasn´t there, so I´m not sure exactly where it is).

Any other ideas?

 

[finntexan]

It is very likely that the problem is caused by a stuck duovalve allowing hot coolant flow into heat exchager continuously. There is a duovalve in engine compartment, just below the wiper arms near the firewall. The duovalve sticks due to the plunger inside getting some stuff on its surface or the electrical short circuit of the coil that moves the plunger. You can clean it yourself, the toughest thing is its removal as it is in place that is not very easily accessible.

I have seen a good thread by a British guy of the reconditioning the rear duovalve, try searching it, it has good pics and all.

Akkurat?