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It 'aint half hot mum...

_Mac Sep 3, 2016

  1. _Mac

    _Mac New Member Team V8 Audi S4 Audi Cabriolet Owner Group

    so, with 4 weeks of ownership under my belt, the air con has suddenly stopped working on my 2004 B6 S4 Cab.

    I think the compressor has gone FUBAR, as VCDS reports 5.0 BAR at rest, only rising to 6.0 BAR when aircon set to LO. I thought this should be much higher? (outside temp measured at 18degC).

    The 2x pipes running from engine bay into cabin are of equal temperature and not that cold.

    Any ideas?
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  3. rum4mo

    rum4mo Well-Known Member

    75PSI at 18C does not sound right for R134A, maybe check what R134A should be at 18C, it does sound like your system has lost a lot of liquid and only has a spot of gas still in it. Maybe time for a pressure test > fix > evac > recharge.

    Edit:- just a note to back that up, all these fridge gases have a saturation pressure at which they start to turn gas into liquid, if a system is just charged with some gas but that pressure is below its saturation point then you will always get a pressure reading that for that temperature, is lower than expected, if that system is correctly charged with liquid, then as long as there is still liquid left in that system, the pressure will be the saturation pressure for that temperature. Typically in a system with a low pressure gas like R134A you can't tell anything from its pressure at rest - other than it might have liquid in it or it has not got liquid in it. Where you can use the pressures is when the compressor is running with a reasonably correctly charged system. That low pressure will stop the compressor running I'd think.

    Another Edit:- that pressure sensor might be faulty though, for pressures, it is best to get someone to fit their gauges on to check that things are what they say they are.
    Last edited: Sep 3, 2016
  4. RJC1980

    RJC1980 Member

    Just had a look 18c is 62PSI, You should ahve around 2 bar (30 psi) on the low side and approx 8 - 12bar on the discharge side when the compressor is running.
  5. _Mac

    _Mac New Member Team V8 Audi S4 Audi Cabriolet Owner Group

    Cheers guys,
    Had the system regassed yesterday but no joy :(
    Will have another look at the pressures on vag-com tonight, as my buddy with a set of gauges is currently on holibobs.


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