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A/C switching off below 4 degrees C.

Discussion in 'Air Conditioning' started by fazzy, Dec 21, 2008.

  1. fazzy
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    fazzy New Member

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    [Dec 21, 2008]
    Hello,
    I'm trying to find out more about this feature in my 1998 A3 TDi.
    The A/C works perfectly well, until the outside temperature falls below 4 degrees centigrade.
    At that temperature the A/C switches off and remains off untill the outside temperature rises above 4 degrees.

    All is well, and the instruction manual says that this is the way it is supposed to work.

    However, I'd like to find a way how to get rid of this feature.
    I would like to have my A/C working all the time irrelevant of the outside temperature.
    Especially between 0 and 4 degrees since at that temperature the windows mist up very easily and a working A/C will prevent that from happening.
    Any ideas, anybody?

    Thanks,
    Fazzy
    #1
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  3. Staz
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    Staz is a retronaut Staff Member Moderator VCDS Map User

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    [Dec 22, 2008]
    Do you have a button to clear the windsceen? Even if the air con is not enabled this will still clear the screen as all the air is directed to the windscreen.

    I doubt you'll be able to change this by the way. The system is designed this way for a reason.
    #2
  4. fazzy
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    fazzy New Member

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    [Dec 22, 2008]
    Of course there is a button to clear the windscreen. Normally, when pressing this button, even when the A/C is turned off, this will cause the A/C to turn on automatically.

    Sure enough if the temperature falls below 4 degrees centigrade the A/C will not turn on and the air directed to the windscreen will be normal air drawn from the outside. Yes, in time (much longer, too long for normal town driving) it will clear the windscreen, but all other windows will still be fogged up as the air is not going through the compressor.

    You're saying that the system is designed this way for a reason. What is the reason?

    In my Jetta and my A6 the A/C works all the time and doesn't switch off below 4 degrees.

    One could also cheat the temperature sensor. Easy and simple to do, amd in this way the sensor will never see the temperature drop below 4 degrees, thus the A/C will never turn off.

    Any ideas about that?
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  5. Staz
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    Staz is a retronaut Staff Member Moderator VCDS Map User

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    [Dec 22, 2008]
    I don't know every single thing about your car by the way.

    Easy done if you know which sensor it is yes.
    #4
  6. fazzy
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    fazzy New Member

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    [Dec 22, 2008]
    Well, basically all Audis since the eighties have a similar windscreen demister regardless of wether it's A/C unit or not.



    That is not the problem. Sensor is easy to locate. I'm more concerned about the condensor and wether it will not freeze when it's say -10 degrees outside.
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  7. Staz
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    Staz is a retronaut Staff Member Moderator VCDS Map User

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    [Dec 22, 2008]

    The refrigerant you mean? It's got to -103 degrees.

    I'm not sure why they have the temp cut out to be honest. I'd have to look into it. May take a while at this time of year.

    It's worth a try anyway. As long as your cut outs are working ok you won't break anything.
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  8. benr
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    benr Member

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    [Dec 23, 2008]
    Well my first thought would be it cuts out because you dont need your air being refridgerated at that temp.

    Also if you find the sensor and you fool it in someway surely this will affect the whole air con system in all conditions? Afaik the system uses cabin temp, outside temp and required temp to work out what settings it will set itself at.
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  9. Staz
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    Staz is a retronaut Staff Member Moderator VCDS Map User

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    [Dec 24, 2008]
    Hmm yes it does use all those different temps to work out what it should be doing. But still as long as you have insuated the outside temp sensor as originally planned the air con shouldn't cut out below 4 degrees.

    But the system could be a lot more complex than that. I just don't know.
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  10. enda1
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    enda1 Member

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    [Dec 25, 2008]
    At 4 degrees water is at its max density and is very likely to turn to ice. The aircon is designed to turn off a 4 C as at this point the water being removed form the incoming air to the air con system could very likely freeze. This means that the water drain from the aircon system could block and then you have the situation that water gets trapped and the air introduced into the cabin is more moist than the outside and you get fogged up windows.
    Living in Ireland which has very humid air i have learned to turn off the air con on wet winter days between 0-4C as I have had the situation where the the drain frezes over and then suddenly the windscreen fogs over.
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  11. Staz
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    Staz is a retronaut Staff Member Moderator VCDS Map User

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    [Dec 25, 2008]
    Aha yes!

    God I'm rusty at this. Not enough practise.
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  12. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Jul 2, 2009]
    More to the point if it freezes, it will eventually burst and destroy a lot of your expensive pipework and A/C components. Why on earth would you want to overide a system that is designed to protect itself? Are you also planning on overriding all your fuses, and removing your rev limiter?
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  13. Staz
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    Staz is a retronaut Staff Member Moderator VCDS Map User

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    [Jul 2, 2009]
    This is an old thread Andy, I'm pretty sure he's decided against it.

    The refrigerant doesn't freeze by the way. Only the water that condenses on the outside of the evaporator and pipes between it and the TEV.
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  14. NHN
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    NHN Retrofitter - Audi - VW - Skoda - Seat Site Sponsor VCDS Map User

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    [Jul 2, 2009]
    He's just trying to catch JoJo's post count :undwech:
    #13
  15. fazzy
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    fazzy New Member

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    [Jul 15, 2009]
    Well, I have removed a rev limiter on several of my cars :)
    But more to the point, if that is the case, then why on earth does the A/C on the A3 switch off and on the Jetta it stays on and I enjoy fog-free windows in winter?

    Staz, I haven't decided against it, just the car will go on sale and I'll get another one. If the story repeats itself, then I'll continue the topic.
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  16. motionlee
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    motionlee Member

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    [Mar 22, 2010]
    To put this to bed, the reason the air con is switched off at 4 degrees is to prevent ice from forming on the evap
    #15
  17. Staz
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    Staz is a retronaut Staff Member Moderator VCDS Map User

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    [Mar 22, 2010]
    Yeah he said that. Over a year ago.
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