W211 Aircon won't switch off - any ideas?

Discussion in 'Electronics' started by Ratz, Jul 29, 2008.

  1. Ratz

    Ratz Hardcore MB Enthusiast

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    I can't get my aircon to switch off on my 2002 E270, is this one of the infamous electrical gremlins? Has anyone had the same problem?
     
  2. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    What do you mean actually, do you mean you cannot switch off your blower or really cannot switch off cooling while driving (the red eco light does not come on)?

    If it is the blower, then it must be the heater blower regulator. I have only seen a couple of these for a W211 though, very "popular" on W210 and other cars of the same age.
     
  3. OP
    OP
    Ratz

    Ratz Hardcore MB Enthusiast

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    Blower is fine it's just the cooling, so in other words I have the light on my AC Off button illuminated but I know the air is still being cooled.

    As it happens this morning I have managed to get it to switch off, but only after messing around with Auto & the AC Off/On button repeatedly. So it seems it's intermittent at best.

    One for the MB garage when the car's next in for service I think. ;)
     
  4. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    This one sounds strange. Do you have the basic AC or the 4-zone option? If it is intermittent, it would be a difficult one for the workshop unless the AC unit give clear stored codes. Could it be just the button? Any youngsters spilling coke on the buttons...
     
  5. Dieselman

    Dieselman Banned

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    There must be a relay for the compressor clutch. It sounds as if that may be sticking on when it should be off.
     
  6. OP
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    Ratz

    Ratz Hardcore MB Enthusiast

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    Basic AC. I know the intermittent ones are always the worst, of course I don't won't to switch it on again for the moment in case I can't switch it off again :rolleyes: . No naughty kiddiwinks, at least not mine anyway - can't speak for the previous owner.
     
  7. benztech

    benztech Member

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    It sounds to me as though your temperature sensor is u/s - it is a replaceble part.
    To confirm this you will need a quick test on a "star" machine which will show the sensor being faulty having an open circiut or short to ground.
    When you have changed the sensor you will again need a star to clear the fault codes.

    Just a thought but in my diagnosis i would check to see if the a/c compressor is kicking in and out. You can do this quite easily you will need someone else. one of you man the a/c controls (on./off) and the other standing in front of the vehicle with the bonnet up.(WATCH OUT FOR BELTS DO NOT LEAN INTO BONNET SPACE WITH LOOSE CLOTHING OR PLACE HANDS NEAR ENGINE)
    You should here a loud clicking noise when the a/c is turned on and off.

    Its not very common on mercs for the compressors to give trouble so i would say its the temp.sensor.
     
  8. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    I thought the compressor definitely did kick in as the owner was feeling the AC cooling the air.

    But shouldn't a temp sensor problem make the AC forced off instead of forced on? Now if it gets forced on, it would make the system freeze at sub-zero temperatures. :confused:
     
  9. benztech

    benztech Member

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    A problem temperature sender would give an implausible reading therefore sending out constant cold air
     
  10. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    OK, can you clarify which temp sensor it would be?
     
  11. alibally

    alibally Hardcore MB Enthusiast

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    If the red light on the EC switch is on all the time and won't go out then there is a fault in the air con system. It should be checked with a diagnostic tester to find out what it is. Also there is a coolant shut off motor thats mounted under the brake master cylinder. This jams up and stops and temperature change in the heater when the controls are moved. Good luck
     
  12. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    Quite true but if the red light is on, the AC cooling is not on which was the problem here. True also that the heat exchanger shutoff valve fails but it is not a correct fix for "cooling always on" to compensate that with enough heating (I mean if the owner really wants AC switched off).
     
  13. Dragon

    Dragon Banned

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    It got climatic control, Merc do away with aircon. The ventilation is always on. The first time you start the engine the climatic control comes on. If you don't want it on, then you reduce the blower speed. If it still comes on then raise the ambient temperature, the blower will stop.:cool:
     
  14. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    I call them all "A/C", sorry for a simple approach, there are too many different ones on different MBs.

    But what car do you have? I've never owned an MB where I cannot switch A/C, sorry, the air conditioning compressor off in a way that it would not stay off when I switch off/on the car. My W221 (211 actually also) has a continuously running compressor (no clutch) but even there I can switch the compressor function off, the compressor then really stops working even if it still rotates.

    I can actually turn everything manual, and air direction and fan speed etc. Doesn't make any sense in my opinion but it can be done and in my car it stays that way. I still don't see this an explanation to the issue from the OP (assuming I still remember and ever got it right).
     
  15. Dragon

    Dragon Banned

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    W211 in my wife car. I don't like aircon or climatic control because it makes me doze off on long distance driving, I must have a sun roof so I get fresh air all year round.
     
  16. s60r

    s60r Member

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    hi,
    my w211 does exactly the same thing. red light is on indicating that ac is off but i know that it isnt as the air is still refrigerated!
    think i will take it in to the dealer while still under warranty.
     
  17. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    The light was changed lately to show AC is actually on when the light is on. I guess this was after MY05 which I understand your car is. I believe the light was also changed from red to something else?
     
  18. corned

    corned Hardcore MB Enthusiast

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    I have a couple of vaguely related questions.

    Firstly, I note that a previous poster states that the W211 has a constantly rotating compressor. Is this why the A/C on or off makes no noticeable difference to the MPG?

    Secondly, what weight of gas should the W211 system accommodate? (Not 4-zone, if that makes a difference).

    Cheers,

    Corned
     
  19. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    I don't have the figure for the second question but switching A/C off does affect fuel consumption on a W211 too. Even if the compressor is rotating all the time, if you switch it off, it is not working (compressing refrigerant) and does not take any power from the engine compared to the case it is running at full power.

    I do not remember the W211 implementation in detail but at least the W221 and I assume the 211 also is using a humidity sensor and the compressor is then used only to reach sufficiently low temperature and sufficiently dry air. Not like the old ones where air is always cooled down to a few degrees and then warmed up according to the actual cooling needs.

    At least a car with the humidity sensor (it might even work without a specific sensor) allows saving energy spent on the compressor. If the ambient temperature is not extremely high, the compressor is not driven hard and there may not be any significant difference in fuel consumption.
     
  20. s60r

    s60r Member

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    :eek: :eek: :eek:

    sorry just to clarify.......when i press "auto" on the climatic, the red light on the "ac off" button goes off. when i hit the "ac off" button the red light comes on - but you say this means the ac is actually ON??!!

    rushing off to read manual as very confused!
     

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