Heating Problem on W124

[Classic_car]

Tried calling mercedes, and they said it could be either one of the things mentioned, Duo Valve, Heater Control Unit or Thermostat. All of which have been replaced, MB man then goes 'book it in which our technician' at a million pound an hour.

I'm still having the exact same problems with my 300se. I am sure it is a matrix (heater core) blockage problem.

The matrix is like a small radiator behind the dash. Basically it gets hot when the coolant is directed through it by the duo valves, the fan then blows air across the matrix, which heats that air and it is piped into the cabin. When the matrix is blocked or partially blocked, the coolant goes mostly elsewhere, rather than through the matrix, so no hot air. Car does not overheat as the coolant is still getting round the rad and engine ok.

I found a place on the net selling a new matrix, for only £75 ish, problem is, replacing it involve removing the entire dash, as far as I can see.. Big job, but I think that's what im gonna have to do, if I cannot unblock mine somehow.

 

[Ade B]

From memory the centre vents on my C124 only ever blew cold air. I thought this was intentional so you could have the heater full on keeping the cabin toasty and still direct fresh air at your face to stop the car getting stuffy.

On cold days I'd just close the vents until the cabin warmed up.

I had aftermarket Diavia AC installed.

I wish my Honda had the same feature.

Ade

 

[rumelk]

I'm still having the exact same problems with my 300se. I am sure it is a matrix (heater core) blockage problem.

The matrix is like a small radiator behind the dash. Basically it gets hot when the coolant is directed through it by the duo valves, the fan then blows air across the matrix, which heats that air and it is piped into the cabin. When the matrix is blocked or partially blocked, the coolant goes mostly elsewhere, rather than through the matrix, so no hot air. Car does not overheat as the coolant is still getting round the rad and engine ok.

I found a place on the net selling a new matrix, for only £75 ish, problem is, replacing it involve removing the entire dash, as far as I can see.. Big job, but I think that's what im gonna have to do, if I cannot unblock mine somehow.

I think im going to have to do the same. Do you know where to source the heater matrix from? also any guides on how to remove the dashboard? I guess everything else has been eliminated, Radiator, Coolant, Duo Valve, Thermostat & Heater Control Panel, the matrix is the last thing remaining.

Thanks for that, and if you send me the link for the new matrix that would be greatly appreciated. we're getting sumwhere:bannana:

 

[kth286]

how did you check the interior thermostats ?

 

[Classic_car]

The link for a place that sells the matrix is

Merc. W126 Saloon (80-90): Car Radiators - CAR COOLING UK - mail order suppliers.

I don't have any guide about how to remove the dash. I was just going to remove the centre console and then keep removing stuff, until I could get to it. I've removed a dash before in a Lotus and that was a big job, I think in the Merc it will be worse.. Still, once that is done, we should not have to worry about the heating and cooling system in our cars for many years

 

[hotrodder]

Dash removal stuff (detail differences as these deal with aircon cars) for when every other possability is exhausted...

PeachPartsWiki: Dashboard Replacement
A/C Evaporator Diagnosis and Removal at W124-Zone.com – A Mercedes W124 Resource Site
83 Climate Control System

Kth286 mentioned the interior thermostats... i thought that setting the temp dials to fully hot (positive click as they hit their stops) set the heater to give it's all regardless of how hot the interior gets.

 

[Ted]

If you suspect a blocked heater matrix, would it be worth attempting to reverse flush it before replacement?

 

[Classic_car]

I've attempted about 5 times! Not sure if i'm doing right, cannot get more than a tiny dribble out the other end. I am putting the hose pipe in the pipe by the oil filter coming from the false bulkhead. Is that the right way round to back flush?

 

[dinoy]

I've attempted about 5 times! Not sure if i'm doing right, cannot get more than a tiny dribble out the other end. I am putting the hose pipe in the pipe by the oil filter coming from the false bulkhead. Is that the right way round to back flush?

disconnect in and out, use caustic soda or something strong (acid) to unblock drains (one shot) do not put too much, if it can take **** out of drains should be able able to clear it.

btw i am breaking e220 might be able to get the matrix out if it is not too much bother, i will look in haynes manual n c.

 

[rumelk]

disconnect in and out, use caustic soda or something strong (acid) to unblock drains (one shot) do not put too much, if it can take **** out of drains should be able able to clear it.

btw i am breaking e220 might be able to get the matrix out if it is not too much bother, i will look in haynes manual n c.

would that be near the duo valve?

 

[kth286]

Kth286 mentioned the interior thermostats... i thought that setting the temp dials to fully hot (positive click as they hit their stops) set the heater to give it's all regardless of how hot the interior gets.

You can turn the dials to fully hot BUT if the faulty interior thermostats are saying the cabin is already up to temp, then NO heat will be generated.

all 124s have fully thermostatically controlled interior heating systems (whether it has air con or not).

So those interior thermostats are vital to the control of heat - check them out.

 

[219]

This needs proper diagnosis rather than trying to fix the fault by throwing a succession of expensive parts at the problem , hoping it will go away .

Since , from reading this earlier today , I recall that you have already flushed and changed coolant , and replaced the thermostat , I will assume that the engine cooling system is OK . Have you flushed through the heater matrix , ensuring free water flow through it ? If the matrix is blocked then you will not get hot air . Next , to determine whether there is a problem with the control system or the duovalve , you need a multimeter - unplug the little connector from the top of the duovalve - now , I cannot remember which pins do what , but generally brown wires are ground - try metering between ground and any other pins - you are looking for a change of voltage when you move the temperature wheels inside the car from hot to cold ( again , I can't remember which way it goes ) but turn both wheels all the way from hot to cold and you should get 12V in one position and 0V at the other end of the scale .

If you cannot get this change in voltages then the control system is not working . If you do get the voltage changes , turn on the ignition but don't start the engine - now get an assistant to turn both the temperature dials all the way from hot to cold and repeat while you listen closely to the duovalve : with the proper voltages being applied it should be easy to hear the solenoids in the valve clicking open and shut - this will be easier without the engine running but normally they are loud enough to hear above the engine idling .

If the valves do not click , but you already know voltage is getting to them , then the duovalve is faulty and needs to be replaced , if the valve clicks but no heat then there is likely to be a problem with water flow through the matrix .

Changing the matrix is a big job , involving removal of the full dashboard , so before that try flushing - you need to disconnect the two hoses from the duovalve which lead to the heater , and the one at the opposite side of the car which goes from the engine block to the heater . These hoses will be roughly the same diameter as your garden hose , so try to find a short piece of pipe or tube of some sort to join them , then turn the tap on and see if water flows freely through ( don't try to force water through the duovalve as it may be closed ) ; try flushing in both directions and only connect back up when you are satisfied everything is clear . If you cannot get free flow of water through the matrix then it will be blocked and will need to be replaced .

Re the cabin thermostats , it is true that they will override a set temperature , but on maximum you should get heat regardless as the valves should stay fully open .

The centre vent is for cold air only to the face to keep the driver alert .

 

[rumelk]

This needs proper diagnosis rather than trying to fix the fault by throwing a succession of expensive parts at the problem , hoping it will go away .

Since , from reading this earlier today , I recall that you have already flushed and changed coolant , and replaced the thermostat , I will assume that the engine cooling system is OK . Have you flushed through the heater matrix , ensuring free water flow through it ? If the matrix is blocked then you will not get hot air . Next , to determine whether there is a problem with the control system or the duovalve , you need a multimeter - unplug the little connector from the top of the duovalve - now , I cannot remember which pins do what , but generally brown wires are ground - try metering between ground and any other pins - you are looking for a change of voltage when you move the temperature wheels inside the car from hot to cold ( again , I can't remember which way it goes ) but turn both wheels all the way from hot to cold and you should get 12V in one position and 0V at the other end of the scale .

If you cannot get this change in voltages then the control system is not working . If you do get the voltage changes , turn on the ignition but don't start the engine - now get an assistant to turn both the temperature dials all the way from hot to cold and repeat while you listen closely to the duovalve : with the proper voltages being applied it should be easy to hear the solenoids in the valve clicking open and shut - this will be easier without the engine running but normally they are loud enough to hear above the engine idling .

If the valves do not click , but you already know voltage is getting to them , then the duovalve is faulty and needs to be replaced , if the valve clicks but no heat then there is likely to be a problem with water flow through the matrix .

Changing the matrix is a big job , involving removal of the full dashboard , so before that try flushing - you need to disconnect the two hoses from the duovalve which lead to the heater , and the one at the opposite side of the car which goes from the engine block to the heater . These hoses will be roughly the same diameter as your garden hose , so try to find a short piece of pipe or tube of some sort to join them , then turn the tap on and see if water flows freely through ( don't try to force water through the duovalve as it may be closed ) ; try flushing in both directions and only connect back up when you are satisfied everything is clear . If you cannot get free flow of water through the matrix then it will be blocked and will need to be replaced .

Re the cabin thermostats , it is true that they will override a set temperature , but on maximum you should get heat regardless as the valves should stay fully open .

The centre vent is for cold air only to the face to keep the driver alert .

Thank you for the information, tried it out and it does seem like my matrix is faulty. Just a few pics here to illustrate what i did:

My next question was do i attach the hose to this pipe to flush out the matrix, besides the battery, it looks like its coming from the cabin so im just assuming it is this one, also you stated it was on the other end of the duo valve. Highlights in pic below:

 

[Orace Hogg]

whilst I appreciate this quite an old thread, I have a question, which I have not picked up on, how do you get the vaneer panel off that is in front of the heater control panel?

 

[hotrodder]

The fan/air direction knobs are a push fit (you might need a rag and a pair of pliers) and there's a 22 or 24mm nut underneath 'em. There are also 2 screws at the base of the trim obscured/partially obscured by the radio.