Cabin air flow in 1995 C220

Discussion in 'Interior' started by mike18hc, Jan 30, 2016.

  1. mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    The problem is poor air flow, hot or cold, although all flaps and fan speed positions seem to work and the pollen filter is nearly new. Unfortunately I don't have a feel for what the fan speed should be as, when it's removed, it seems to spin properly.
    There's web info for the W202 LHD heater box but I haven't found any on for RHD.
    If the evaporator matrix is partly blocked would that reduce both the hot and cold air flow?
    Where would a blockage have that effect?
    Does this model just have poor air flow by design?
    What I'm trying to find out for sure is how the air gets to the fan and then through the vents, and where the heater matrix and evaporator sit in the scheme of things.
    Can someone point me in the right direction please?
     
  2. Dec

    Dec Hardcore MB Enthusiast

    Messages:
    4,475
    Joined:
    Jul 28, 2004
    Car:
    C180,A.
    Air flow should be good and not give rise to complaint either hot or cold and in all directions.

    Do you have automatic or manual heater control unit?
    Manual… Heater control panel

    Dec
     
  3. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    Tempmatic temperature control panel

    The controls are manual - 2 thumbwheels for temperature, 2 rotary switches for fan speed and direction and 4 pushbuttons for defrost/rest/ec and recirc.
    Temp control is fine as are directions. Speed positions do change fan speed but there's little air coming through. Defrost doesn't defrost much (a fogged-up screen can take 10 minutes to clear), rest gives some warmth when the engine's off, ec cuts out a/c and recirc operates a flap that results in a large increase in air blowing noise but no increase in air flow. I assume the noise increase is due to the air intake then being inside the car and not outside.
    This is the way the car was when I got it 10 years ago and I did start to believe it was normal.
    Air through the side window vents, fully open, at full speed can be detected by hand about 5 inches away. The other vents are very similar but the screen vents' air you can feel around 6 inches away!
     
  4. Dec

    Dec Hardcore MB Enthusiast

    Messages:
    4,475
    Joined:
    Jul 28, 2004
    Car:
    C180,A.
    From your description, the air flow sounds ok and it is the defogging of the windscreen that is the real issue, it should not take 10 minutes to clear.
    A fogged-up screen should take about 30 to 60 seconds to clear, if your air con is OFF (EC Red light on) or if the air con is not working properly then it will take a lot longer to clear.
    Air con should be on all the time, summer and winter.

    When the REST button is used, the outside air intake flap closes and it is the cabin air that is recirculated so that might explain the extra noise alright.

    The engine temperature should rise to just above 80c after about a 3 mile drive, is that correct in your case?

    Dec
     
  5. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    The coolant temp rises to 80C quite quickly and after maybe 10 minutes, even with what I think is poor air flow, the car's relatively comfortable to be in.
    The air noise level changes only when recirc is pressed, but there's no more air moving then than with the exterior flap closed.
    With REST I can't detect fan noise, which suggests the air's convected.
    As you say, defogging is a real problem in this car.
    The A/C is always switched on but I assume the compressor only works when cooling's needed, ie it'd be on if demisting's chosen or when a lower temp is dialled up.
    Obviously air goes through both the evaporator and heater matrix, but it can't go through both in sequence since unheated air comes from the shared centre vents but heated air comes from all the other ones.
    Online there's a drawing of the air flow through a W203 showing flaps controlling evaporator and heater air separately.
    Does my system have flaps other than those which divert air directly to the outlet vents and the inner and outer inlet vents?
     
  6. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    Just to clarify why I mentioned the centre vents.
    My car's owners manual says the centre vents output unheated air when EC's pushed and that also goes for cars without AC fitted. The implication is that the air then doesn't come from the heater box.
    How?
     
  7. Dec

    Dec Hardcore MB Enthusiast

    Messages:
    4,475
    Joined:
    Jul 28, 2004
    Car:
    C180,A.
    The compressor is ON when the aircon is on (Red light OFF on EC switch) regardless of whether the heating is set to hot or cold or if demisting is chosen.

    [​IMG]

    There is a sometimes a perception that car air con should be used only on hot summer days and is for cooling only, it is recommended that it should be used all year round.
    If it takes 10 minutes to defog the windscreen then either the A/C is not ON or it is faulty.


    Dec
     
  8. Dec

    Dec Hardcore MB Enthusiast

    Messages:
    4,475
    Joined:
    Jul 28, 2004
    Car:
    C180,A.
    I had a 1995 with no air con and cold fresh air only came out of centre vents, does your EC switch light up when pressed?

    Dec
    [​IMG]
     
    Last edited: Jan 31, 2016
  9. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    Yes it does light up.
     
  10. Dec

    Dec Hardcore MB Enthusiast

    Messages:
    4,475
    Joined:
    Jul 28, 2004
    Car:
    C180,A.
    Check to see if the compressor is rotating while the engine is running.
    As illustrated in the picture below, you will see the outer part rotating when the air con is ON, it will be stationary when the air con is OFF.

    Dec

    [​IMG]
     
  11. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    The clutch does operate correctly and can be operated off and on by the EC button.
    All the basics seem OK except that the amount of air is poor.
    For comparison I tried my Cavalier's heater's air flow and that really blows a gale. You can feel the draught 2 feet away from the vents!
    Tomorrow I'm trying an R reg C200 to get another feel for what's normal in an old similar Merc.
     
    1 person likes this.
  12. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    This isn't what I expected. The C200's air flow's just like my C220's, almost non-existent!
    Still, I'll do due diligence on mine, take off a footwell vent cover and the central vent cover and look around past the flaps with my Snakescope to see what's happening in the heater box.
    Since all vents are equally affected, looking at two should be enough to prove flaps are operating fully.
     
  13. Dec

    Dec Hardcore MB Enthusiast

    Messages:
    4,475
    Joined:
    Jul 28, 2004
    Car:
    C180,A.
    Tell us more about this Snakescope, sounds like something I might need.

    There is another way into that area from the outside of the car, this is through the outside air intake opening/flap, you can see where I mean at 3 minutes into the video beloe.

    Dec

    https://www.youtube.com/watch?v=C_LeuzB36dQ

    [YOUTUBE]C_LeuzB36dQ[/YOUTUBE]
     
  14. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    Snakescope

    Amazon describe it as a USB Powered Flexible Camera with LED Light. It's a borescope with a 2-foot flexy tube so it can be used to find lost items in hard-to -get-to places, as long as you're happy to have a pc in close proximity so you can see the screen image it produces. Used under cover it's quite useful.
    I see the price has doubled since I bought mine!
     
    1 person likes this.
  15. DaveLondon

    DaveLondon Active Member

    Messages:
    76
    Joined:
    Jan 26, 2016
    Car:
    CLK430 Avantgarde Convertible, BMW 330ci Sport Coupe
    A random thought, but have you changed/inspected your cabin air filter recently? It's a quick job, and a blocked/old filter might be causing your lack of airflow...
     
  16. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    How I wish it was!
    Unfortunately it's quite new and looks good.
    Leaving it out made no noticable difference to the air flow.
     
  17. OP
    OP
    mike18hc

    mike18hc Active Member

    Messages:
    94
    Joined:
    Jul 26, 2006
    I think I won't be able to improve the airflow on this car. It is what it is and I'll have to live with it but at least I've found a ventilation fault.
    The central vent is almost closed...when it should be open that is. The dash isn't coming out so I'll work round that and call it a day.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.