W202 Heat is either hot or cold... no warm

Discussion in 'Interior' started by dude99, Sep 24, 2015.

  1. dude99

    dude99 New Member

    Messages:
    4
    Joined:
    Nov 10, 2013
    Car:
    1997 E290TD
    Hey all, Trying to sort out the heat on my GF's 1999 C230 Kompressor. It is the "Classic" trim level so it has the twin temp knobs and the dials for the blower and vents, not the digital climate control system fitted to many of them

    The passenger side previously worked fine and the heat modulated as you would expect. The drivers side has always either blown cold or hot, there is no warm section on the dial. Its like it just flips over from full cold to full hot, and now both sides are doing it.

    I have disassembled and cleaned the duo valve and it made no difference to the issue. I'm assuming at this point it is working as I can get either hot or cold on each side so the valves must be opening and closing.

    If you leave it in the middle section of the dials it will flip flop back and forth, scorching hot for a bit, then cold for a bit with no particular pattern.

    I've done some hunting, and some looking at the components of the system on the EPC and am thinking that it may be the actuators that control the mixing flaps in the airbox. Only thing is I can't find a way to access them, or where the vacuum manifold is for this system.

    All help is appreciated as I'm rather stuck at this point.

    P.S. This is a Canadian market car. The reason I chose to pose this question to your forum is that it is a C230 Classic model (with the rotor knob climate control). Most forums for North America are most frequented by people in the US who did not receive this model (all of theres came with the digital climate control unit as far as I'm aware). So since I've been lead to believe this system is commonplace in the UK I'm hoping you can help.
     
  2. andy27168

    andy27168 Hardcore MB Enthusiast

    Messages:
    4,352
    Joined:
    Nov 27, 2004
    Location:
    Southampton
    Car:
    1997 C230K, 1999 C43/55 AMG
    Hi,
    The dial type heater controls do not have actuators or require vacuum, as moving the dials themselves adjust the flaps etc, the dials themselves are keyed on shafts directly to the heater box.
    I had a similar issue on my 202 and it was the heater control unit itself that was faulty, there is a small temp. sensing fan in the interior light behind the small grill which can cause issues but normally becomes noisy.
    The heater temp dials I believe are just rheostats and can become dirty so it may pay to spray some good quality switch cleaner first, but if that doesn't solve it I would be looking to replacing the control unit.
    If you look on E-bay there are quite a few breaking and listed as they quite expensive new from MB.
     
  3. OP
    OP
    dude99

    dude99 New Member

    Messages:
    4
    Joined:
    Nov 10, 2013
    Car:
    1997 E290TD
    My EPC shows two vacuum actuators for the mixing flaps (one for each side of the car).... The dials, which are just rheostats you mentioned, must control some sort of actuator as they themselves don't physically move the flaps.

    By control unit do you mean the entire switch assembly?
     
  4. OP
    OP
    dude99

    dude99 New Member

    Messages:
    4
    Joined:
    Nov 10, 2013
    Car:
    1997 E290TD
    bump.... "winter is coming" need heat
     
  5. Dec

    Dec Hardcore MB Enthusiast

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    4,475
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    Car:
    C180,A.
  6. OP
    OP
    dude99

    dude99 New Member

    Messages:
    4
    Joined:
    Nov 10, 2013
    Car:
    1997 E290TD
    before I throw parts and $$$ at it I'd like to confirm what the problem is, thats why I'm interested in knowing what controls the two vacuum flaps, I'd like to see if they hold vacuum. That way I know if its a control issue or not.
     
  7. Dec

    Dec Hardcore MB Enthusiast

    Messages:
    4,475
    Joined:
    Jul 28, 2004
    Car:
    C180,A.
    My understanding is that flaps don’t control temperature, only the air direction to the windscreen or to the floor.

    The temperature is controlled by the position of the thumb wheel;
    Red = duo valve open constantly.
    White = duo valve oscillate open and closed so you have ½ hot ½ cold = warm.
    Blue = duo valve closed constantly.

    When the car is up to full normal working temperature, ignition on, engine off, and with the thumb wheel set at White the duo valve should vibrate as it oscillates open/closed and you should hear a clicking as demonstrated at time line 8.30 on the video below.


    https://www.youtube.com/watch?v=8jhPEfLI45s

    If you cleaned the duo valves then the chances are the are both good so that leaves the heater control unit, you would have to take that apart to investigate further.
    An insight on how it comes apart… How to repair bulb failures in the heater panel - Mercedes-Benz Owners' Forums


    Dec
     

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