W124 Heater Problem

[Sean W124]

Hi, my 1996 W124 E220, without climate A/C, has a heater problem. It only blows cold air from the central vents, always blows hot onto the screen and out of the side dash air vents and a bit of heat into the foot well. It doesn't seem to matter where the heat direction knob is.

I have dismantled and cleaned the duo valve: no change. Does anyone have any ideas?

Thanks
Sean

 

[SilverSaloon]

on standard "turn knob" W124 you only get fresh air from the centre vents, non heated. this is as designed.

my "push button climate control" w124 you get hot air from centre vent but not much, but get strong cold. it appears to lock off cold air better than in the knob version.

 

[GP801]

Cold air from the centre vents is normal. Do you mean you cant control the direction/volume of the air supply to the other vents or cant control the temperature? Sorry if I am being stupid here.

 

[balge]

If the flow direction control doesn't work the flaps aren't being moved properly at a guess? Never had a dash out, but presumably there's a broken/disconnected linkage somewhere.

 

[millo777]

As other have said, the centre vents supply only non heated air by design. The owners manual refers to them as "Swivel vents for non heated fresh air".

 

[Sean W124]

Thanks for the info regarding the centre vents. The main problem is that I always get hot air out of the demister vents under the screen and the side vents regardless of where the direction knob is. Also, the hot into the foot well is very weak. I do not know how it works; under the bonnet there is the duo valve as well as a bigger single silver coloured solenoid valve in front of it - do these control air direction? Balge suggests a problem with flaps - does the 124 use these (and if so, where are they). I haven't managed to find a schematic so I'm in the dark. Any help is gratefully appreciated
Thanks
Sean

 

[balge]

The duovalve controls how much hot water goes to each side of the car - each side is controlled by the relevant heater dial. If heat is going to both sides then the duovalve is working.
There is only one fan so if the fan is working, the only other component is the trunking and control flaps? Is the fan blowing hard?

DIY for manually controlling center and footwell vents in a W124 - Mercedes-Benz Forum

The automatic a/c models use vacuum pods to control the ducting, but I believe the 'manual' a/c and non-a/c models are mechanical linkages?
Might be wrong, as I said, never actually been in there...will be interested to find out!

 

[GP801]

Similar issues with ours although could not get any air to the screen. The cables/linkages had come adrift. Not quite sure exactly how they had broken but the dealer had come across it a few times before. New cables etc were £30 or so but its a dash out job to fix it. I sincerely hope its not that.

 

[3 phase]

The automatic a/c models use vacuum pods to control the ducting, but I believe the 'manual' a/c and non-a/c models are mechanical linkages?
Might be wrong, as I said, never actually been in there...will be interested to find out!

Mines a manual AC model and it has vacuum pods to control the ducting, found that out when one of the vacuum pipes got knocked off when refitting the inlet manifold.

 

[Cleggmeister]

I have the same specification as the OP. To block off the cold air from your centre vents, assuming the roller 'knob' doesn't work, look at the rightmost vent and you'll see a screw with an allen key head. Turning this will almost fully close airflow from the centre and should improve flow from the others.

 

[Sean W124]

It sounds like it might be the cables though it appears to have a dealer fit manual A/C (the markings on the buttons on the dash have worn off) so I will check for vacuum pipes as per Cleggmeister's message - do you know where I will find them?
Thanks

 

[balge]

Mines a manual AC model and it has vacuum pods to control the ducting, found that out when one of the vacuum pipes got knocked off when refitting the inlet manifold.

Hmm, mines a dealer fit a/c, wonder how that works...

cheers

 

[Vlad]

Up by the sunroof switch there is a little vent with a mesh over it. Behind this there is a sensor that senses the heat in the cabin. Check that the vent isn't full of dust and lint....mine was and confused the sensor and the heating system always blew hot. Once cleaned out everything went back to normal. Worth a check