Suzdalov

I have 1996 S320, it works fine then I stop at a light and all of asudden it starts blowing hot air on the side vents and windshield while still blowing cold in the middle vents, it also blows cold all the time to the rear from between the two seats and I cant stop by a switch on the face of the rear outlet it just keeps blowing.................I turn it off for a bit and sometimes it fixes the problem for the front, but rear always blows cold and you can't stop no matter what. sometimes it doesn't fix it and i have to drive without climate comtrol for the whole day......even in the winter it blows to hot...............almost frying you up......so i have to turn it off..............The rear vent is only ment for cold air and it just might be a problem with the swith......but the climate control for the front seats is behaving weird. .......It also has a fault code for low voltage ........not sure if it has anything to do with that. It gives a code "FUSE F2 or ECU (N16/D) malfunction.....set range blower motor"............what everthat means..............i'm sure it has something to do with hot air.

Suzdalov

Flashed my cooling system and that seems the have fixed it for the most part............not sure why............but had it happen only twice in two weeks after that...................

twr

I have a 97 S420. The side vents intermittently blow hot air on a 90 degree day. If I shut off the side vents and push the blue button on the middle vents it's tolerable (barely). Any ideas?

mercedestech2

Your duovalve is probably sticking. This valve controls coolant flow to the heater core. If fluid is slightly bypassing this valve you will never have cold air. If the valve fails electrically or mechanically the default value is hot to protect the engine cooling system. The valve is located on the d/s under the hood underneath the cosmetic cover.