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W210 300td very poor heater

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by Ian Parkin, Nov 21, 2012.

  1. Ian Parkin

    Ian Parkin Senior Member

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    Your Mercedes:
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    I have a 1997 300td 606 engine with air con fitted
    The heater suddenly has become very poor not really used it much this year
    engine gets up to temp 85-90 ish ok
    very faint heat comes out of drivers side nothing out of passenger side

    fan works well...good blast of air out of vents but no heat

    where do I start?

    does the circulation pump run at all times? thats the one just before the duovalve

    any pointers?

    ian
     
  2. mersum1es

    mersum1es Senior Member

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    duovalve jamming
     
    Last edited: Nov 21, 2012
  3. Frontstep

    Frontstep Senior Member

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    Last edited: Nov 21, 2012
  4. Dec

    Dec Senior Member

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    Bring the car up to normal temperature, unplug the duo valves as in picture, give both valves a gentle tap with the head of a screwdriver and leave the valves unplugged for a day or two.

    The circulation pump runs only when the ignition is off and when the recirculation switch is turned on.

    Dec

    [​IMG]
     
  5. OP
    Ian Parkin

    Ian Parkin Senior Member

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    Many thanks will try that tommorow

    Ian
     
  6. OP
    Ian Parkin

    Ian Parkin Senior Member

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    No real difference after disconnecting and tapping the valves
    the other thing i have noticed is that while the top hose on the rad is hot the pipes going to the duo valve ( from the engine and back to the engine) are quite cool,shouldnt these be hot to touch?
     
  7. Dec

    Dec Senior Member

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    If the duo valves are stuck shut then no hot water can circulate through the heater so the small hose gong to the duo valves should be cool/cold even after driving several miles.

    Give it another day in case the valves free themselves.
    Are both sides, passenger and driver, of the car cold?

    Dec
     
  8. OP
    Ian Parkin

    Ian Parkin Senior Member

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    Drivers side is warm but if i run the fan on high speed the air flow runs cold after 30 seconds or so...
    when the duo valves are shut mind wont the hot water still circulate through the feed and return pipes ? only on opening both duo valves will the hot go through the respective heater matrixes rather than back to the engine?
    2 pipes in to one side of duo valve and 2 pipes on the other side...its the inlet pipes that are not getting hot
    Ian
     
  9. Dec

    Dec Senior Member

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    Drivers side is warm but if i run the fan on high speed the air flow runs cold after 30 seconds or so... so too much air flow, driver side must be slightly open if you are getting some warm air.

    when the duo valves are shut mind wont the hot water still circulate through the feed and return pipes ?... no, but some water is getting into the driverside valve as above.

    only on opening both duo valves will the hot go through the respective heater matrixes rather than back to the engine?... correct.

    2? pipes in to one side of duo valve and 2 pipes on the other side...its the inlet pipes that are not getting hot … There should be one pipe going into the duo valves and 2 pipes comeing out and on to the heater.
    Ian

    Dec
     
    Last edited: Nov 22, 2012
  10. OP
    Ian Parkin

    Ian Parkin Senior Member

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    Yes 2 pipes the one on top goes back into the engine bay and then towards the back of the engine and the bottom one comes from the circulation pump and out of there towards the water pump/thermostat area.

    You can clearly see the 2 pipes in your photo the ones that go to the heater matrix are side by side under the electrical plug ?
     
  11. Frontstep

    Frontstep Senior Member

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    Follow my earlier link and clean the valves.
     
  12. OP
    Ian Parkin

    Ian Parkin Senior Member

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    Right I've removed the circulation pump from the system and fitted a short section of pipe instead of it.
    On starting the engine no water flows with a positive pressure

    the pump doesnt work on applying 12v so i stripped it down and the brushes are worn to excess

    are we sure that the pump only works when the residual heat switch is pressed because i also have 12v at the plug when engine on

    I have never used the residual heat button ,cant imagine many do, so why are brushes worn?
    euro car parts sell this part at £85

    If this pump was working i may get better heat transfer to the duo valve?
     
  13. OP
    Ian Parkin

    Ian Parkin Senior Member

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    Frontstep

    I'm fairly sure that the duovalve is ok its just not getting hot water to it....
     
  14. Dec

    Dec Senior Member

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    The residual heat pump is used to keep, for example, your Granny warm if you are away from the car for a while, the pump will recirculate the hot water in the heating system through the heater, the fan will come on and blow warm air into the cabin and keep it warm. This will last for about 30 minutes.

    It will not work if there is insufficient charge in the car battery or if the temperature of the water is very low.
    The residual heat pump will have no bearing whatsoever on your lack of heat in the cabin, your problem would seem to be that the duo valves are stuck closed, as an alternative to taking the valves apart, so as to free them up, we are waiting to see if the will free themselves up on there own… hence the suggestion to wait a day or two.

    Taking the pump apart won’t do anything to solve the fault, it may be that you will have to open the valves as per the guide linked in page 1 to solve your fault.

    Keep the vales disconnected for now, a merical may happen over night.

    Dec
     
  15. OP
    Ian Parkin

    Ian Parkin Senior Member

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    I know that the pump comes on if you want the cabin to be warm after you have stopped but also the pump HAS to run with the engine to allow water to get to the duovalve...if i remove the pipe going to the duovalve and start the car theres no flow...no flow means no hot water therfore no heat to the matrix...this pump has to run with the engine..perhaps if you are only wanting cold air it could switch off perhaps

    I've ordered a new pump we will see if that works

    Ian
     
  16. Dec

    Dec Senior Member

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    Attached Files:

    Last edited: Nov 22, 2012
  17. OP
    Ian Parkin

    Ian Parkin Senior Member

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    Yes looks the same as that
    but you said your duo valve only has 3 pipes going to it.

    I know that the pump has to run for residual heat
    but in my cars application it surely has to run all the time hence brushes worn out
    theres no other way to get hot water to the duovalve other than by thermo-syphoning
    which is whats giving me slightly warm heating
     
  18. OP
    Ian Parkin

    Ian Parkin Senior Member

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  19. Frontstep

    Frontstep Senior Member

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    I am confused with that, the other pump mentioned is the main water pump isn't it.
     
    Last edited: Nov 22, 2012
  20. Dec

    Dec Senior Member

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    The only time my pump will run is if the engine is off, when the engine is running then the engines water pump drives water through the system, if the duo valves are open, then hot water will reach the heater… in your case your duo valves seem to be stuck shut.
    The picture below relates to a different issue bur illustrates the rout water (in Blue) takes around the heating system.

    Dec

    [​IMG]
     

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