Heater problem - not Duo valve

[tom1995e220estatew124]

The heater on my 1995 E220 Estate W124 is only blowing hot out of the passenger's side. I thought this was the fault of the Duo Valve and bypassed it with a Y piece and some customised plumbing. Still the same. If the fan is not turned on the driver's side matrix will heat up but will then go cold when I turn on the fan. I believe this to now be a circulation problem. When the Duo Valve was on I closed the passenger's side and took the hose off the driver's side but circulation looked bad. Is there anything I need to do to successfully flush through the system or is there another problem? It is almost freezing on the driver's side and my girlfriend is complaining it is too hot on her side and she wants to open the window !!! Help appreciated.

 

[Dec]

Don’t know anything about your particular car but this sounds like an issue with flaps stuck open or the knob that controls them.

Put your VIN number in here... http://www.detali.ru/cat/oem_mb.asp then there should be a link at the bottom of the page you are brought to which will bring you to more links to drawings of the heater assembly.

Sorry I can’t be more helpful but this might give you some ideas.

Dec

 

[kth286]

But you have a temperature dial for each side, and this is on the dash.

Turn your's up a bit (to make your side hotter), and turn her's down a bit (to make her side cooler).

Is there any problem in doing that ?

Let us know how you get on.

 

[tom1995e220estatew124]

Thanks

Dec thanks for the link to the parts catalog.
David thanks for the suggestion but the individual heater controls / dials no longer work because I have bypassed the Duo Valve. I drove the car round the block and the controls no longer seem to work.

 

[Dec]

As far as I know the dials open and close the Duo Valve's. I assume you were aware of their function before you “re-plumbed” them. That still leaves the flaps, maybe removing something like the radio? might allow you to get your hand in for a feel around for flaps that may be open or closed, that’s why I suggested looking up a drawing of the heater on that Russian site.

Dec

 

[tom1995e220estatew124]

Flaps?

Hi Dec, after David's suggestion about the dials I drove round the block and got the car up to 90 degrees. I played with the dials but they didn't seem to affect the temperature. The passenger's side was still hot (ish!) whilst the driver's side was still cold. The flaps you mention. Are they governed independently. If they are not connected to the dials how do they know whether to let in hot or cold? Apologies if these are obvious questions.

 

[Dec]

Hi Tom
I am not an expert, but in the absence of any other advice, this is how I believe the heating works.
Hot water is pumped up to the two Duo Valves, one valve for the driver side and one valve for the passenger side, if both dials (passenger and driver) are set to HOT then both Duo Valves open allowing hot water into the heater matrix (kind of small radiators) which then returns to the engine block via one rubber hose.

If a dial is turned down to COLD, for example on the passenger side then that Duo Valve closes preventing hot water getting into the passenger side of the heater matrix. The heater matrix is in two halves i.e. one for passenger and one for driver hence the need for two Duo Valves.

If the two Duo Valves are working properly then BOTH rubber hose coming from the Duo Valves to the heater should be hot, assuming of course that the engine is hot (and both dial’s being set to HOT) if this is the case then your Duo Valves are working o.k. Just to be completely sure it is not the Duo Valve on driver’s side, drive the car at about 50mph with the fan set at off, BUT NOT AT 0 you should feel hot air coming in through the vents depending on your speed.

Quote;“The flaps you mention. Are they governed independently. If they are not connected to the dials how do they know whether to let in hot or cold?”

They flaps are governed independently of the dials but serve both passenger and driver sides, the dials just open / close the Duo Valves depending on whether the are set to red, white or blue (hot-cool-cold)
The flaps are controlled by the “clock” type dial which when pointing to the East or 3 o’clock side allows you to direct the hot air to the windscreen or to your feet in winter.
If this dial is pointing to the west or 9 o’clock side then you are getting exclusively fresh air from outside the car for summer use.
The fan dial just increases the volume of air coming into the car, if it is set to 0 then no air comes in.

So if it is not the Duo Valves or if the drivers side of the matrix is not blocked then it must be something to do with the flaps. It might be useful if you could put up a picture of the heater workings from the Russian site here. I am unable to access the Russian site myself as I have some security software that will not allow me on to it, and which I am still trying to figure out.

If you were to back-flush the heating system you would take off the return hose going into the engine block and attach a garden hose to it and remove the two hoses going into the Duo Valves, however I have no idea how effective this would be.

Dec

 

[wireman]

The matrix is likley to be partialy blocked, you might be able to flush it but it is uncommon for this to be effective. The crud from the coolant can collect in the matrix and block some of the water tubes leaving some clear (which will hog the flow) this leaves only part of the outer finned air suface heated and this gets cooled rapidly by the fan assisted airflow, best cure is a fresh matrix.
Changing coolant at no longer than 3 years helps to avoid this problem occuring, especialy if the rest of cooling system has had problems.

 

[kth286]

Just as an aside (in case it makes a difference to your thinking), the far end dash vents admit hot air depending on the temperature dioal setting for each side BUT the centre dash vent ONLY EVER admits cold air. This can be turned off (or partially off) by use of the dash vent flap itself.

 

[tom1995e220estatew124]

Spoke to a Merc guy yesterday and he asked me if the car had ever had a head gasket replaced. Not definite but there was a new rad on the car when I got it and the viscous coupling for the fan was faulty causing the engine to overheat in traffic. It may have had a bad boil up and needed a new head gasket. The previous owner didn't mention when I bought it. Anyway, the Merc guy said he had seen quite a few that had head gaskets replaced that developed heater problems because of oily residue in the heater matrix. He said that this could not be shifted by normal flushing through and required a serious chemical Radflush to rectify. I've done a normal two directional flush through of the matrix and it definitely improved the situation. The heater does now get hot on the driver's side but if I have the blower on full for any length of time it goes cold again. So, still not great circulation. The residue theory seems to make sense. Hope this helps anyone else with a similar problem. Flaps are OK. Thanks for that suggestion and thanks to all of you for helping. Much appreciated. Merry Christmas and Happy New Year. Best wishes. Tom

 

[television]

Dont forget the pump 140 in the link

http://www.detali.ru/cat/oem_mb2.as...GM=717.413&CT=F&cat=15T&SID=83&SGR=180&SGN=04

 

[kth286]

tom

Mercedes themselves have made a cooling system flush available since the head gasket problem first started on the 103 engine.

Not many people seem to be aware of it and indeed it is essential for the system to be cleaned of oil to prevent the rubber hose pipes from bursting because they get soft with oil.

Part number is 001 986 21 71

You need to use a 3% solution.

Run engine for 10 minutes before completely flushing the cleaner out of the radiator with clean water.

The heater must be on and running to clear the oil from the heater core.