Rear cooling/heating help (W219 - heater control valve?)

Discussion in 'Parts, Maintenance & Servicing' started by moodi, Dec 2, 2018.

  1. moodi

    moodi Hardcore MB Enthusiast

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    Looking for some help. My new-to-me W219 CLS 55 has an issue where the rear is hot no matter what the control dial is. The front heating/cooling works fine.

    I have read that it could be the heater control valve, as this topic:

    [SOLVED] - Rear Aircon Hot Hot Hot!

    However, the last reply leaves me less than confident.

    What is the best way to diagnose / fix this?
     
  2. whitenemesis

    whitenemesis MB Club Veteran

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    Bet way? Get the codes read using STAR
     
  3. OP
    OP
    moodi

    moodi Hardcore MB Enthusiast

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    I've also heard it could be this. Would STAR tell me for sure?

     
  4. clk320x

    clk320x MB Club Veteran

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    Wouldn’t this be a duovalve issue?
     
  5. OP
    OP
    moodi

    moodi Hardcore MB Enthusiast

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  6. clk320x

    clk320x MB Club Veteran

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  7. OP
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    moodi

    moodi Hardcore MB Enthusiast

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    I think access is even more tricky on the W219, the wipers/motor/assembly need to come out from what I have seen?

    The part is cheap enough, but just wondering if there is a definitive diagnosis before I chuck some cash at it. STAR could be an option if someone can confirm it will show one way or the other.
     
  8. clk320x

    clk320x MB Club Veteran

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    Mine didn’t have any errors on star for the duovalve

    But if you are having hot air in the back and cold in the front it’s 99% going to be the duovalve
     
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  9. OP
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    moodi

    moodi Hardcore MB Enthusiast

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    That is exactly what the symptoms are. Ok, a £30 part and 2 hours of DIY with some buddies, doesn't seem too bad for troubleshooting at minimum and hopefully a total fix!
     
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  10. clk320x

    clk320x MB Club Veteran

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    Good luck pal! Also I have replied to your pm :)
     
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  11. AMGeed

    AMGeed MB Club Veteran

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    My indy changed my heater control valve. Same symptoms, hot and cold at the front, hot only at the rear.
    He removed the accelerator pedal and moved the SBC pump a bit to gain more access and did the job in around 30 mins. (Prior experience counts a lot I'd say)
    This is the state of mine when it was opened up.
    8KMLgrE - Imgur.jpg hcj4K00 - Imgur.jpg
     
  12. OP
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    moodi

    moodi Hardcore MB Enthusiast

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    Accelerator pedal and SBC pump? Guessing yours was not a W219? (think they are in a different position)

    Yikes! I'll cut mine open if this cures it and see how bad it is compared.
     
  13. clk320x

    clk320x MB Club Veteran

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    The 211 and 219 are basically the same underneath.

    I’m not sure how removing the accelerator pedal will help Rog as surely the firewall is in the way?
     
  14. Major774

    Major774 Hardcore MB Enthusiast

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    It will most likely be the duo valve, I have personally changed mine myself as the rear vents were blowing hot air.

    In the meantime, you can trick the system to work when you get the hot rear vent issue. If I remember correctly, turn the front two temp. settings to high and run it until you feel cold air blowing out the rear vents. Then you can lower the front temps and the rear vents should keep cool.
     
  15. AMGeed

    AMGeed MB Club Veteran

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    Yep, I thought it strange but it made access so much quicker.
    The 219 shouldn't be any different to my 211 for this job.


    Thats the way an experienced indy did it Abs. I wasn't going to argue.
    What made it worse for the poor guy, the OEM valve supplied was faulty and he had to do it twice.:wallbash:
     
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