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S4 B5 Heated mirors..

Discussion in 'A4/S4 forum(B5 Chassis)' started by s4best4, Nov 14, 2010.

  1. s4best4
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    s4best4 Member

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    [Nov 14, 2010]
    Hi there-can anybody tell me if the heated mirrors on my facelift S4 are always on? I assumed they only came on when the heated rear window was on(like on my old S2) but mine are always on! I had a slightly embarrassing experience a couple of weeks ago when my friendly MOT man became slightly less friendly as he leaned against my drivers mirror and yelped cos it was so hot! i assume there's a thermostat not working, but I was surprised it was on at all as the HRW was off?
    Any info greatly received.
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  3. Blue_Thunder
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    Blue_Thunder Active Member

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    [Nov 15, 2010]
    Think pre-facelift are always on. Facelift cars only came on either at a particular temperature, or with the rear windscreen heater, can't remember which.
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  4. jcb
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    jcb Active Member VCDS Map User

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    [Nov 15, 2010]
    mine are always on (99 facelift),
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  5. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Nov 15, 2010]
    very early cars (95-96) had them hooked into the rear heated screen switch.

    Everything else supplies continuous power to the mirrors.

    Some people say that facelift cars have some sort of thermostat built into the glass, however this certainly isnt shown on any Audi diagram, and i suspect its there to kill the power once the glass reaches a set temperature, a bit like the cutoff switch inside a kettle, rather than to turn them on when its cold.
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  6. s4best4
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    s4best4 Member

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    [Nov 15, 2010]
    Thanks for that everyone. I think there must be some sort of thermo cut out as the drivers side gets really hot and passenger is normal temp. At least its probably not a wiring fault that I really don't want to tackle...
    Thanks again for your help.
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  7. GSB1
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    GSB1 Member

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    [Nov 15, 2010]
    The later mirror glass has a thermostat on the back, it is plain to see. The glass does not heat unless it is cold enough.
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Nov 15, 2010]
    Well mine certainly get warm even on the mildest of days.

    I suspect its a bi-metallic strip, designed to cut the power once the glass has heated up, rather than being designed to only power the glass up when it gets cold.
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  9. jcb
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    jcb Active Member VCDS Map User

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    [Nov 15, 2010]
    ah, now by complete coincidence i just pulled one of these off today.
    there is a sensor about the size of three 5p peices stacked in one corner.

    the one I replaced it with didnt have one so I presume that it is dependant on the glass you put in them
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  10. andybnwc
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    andybnwc Member

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    [Nov 16, 2010]
    Also the mirror adjuster has to be in the centre too i think
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  11. GSB1
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    GSB1 Member

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    [Nov 16, 2010]
    The thermostat (sensor or whatever) breaks the circuit, unless it is cold enough, then the circuit completes and the mirror element heats.
    #10
  12. GSB1
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    GSB1 Member

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    [Nov 16, 2010]
    Exactly. Early glass did not have this, original replacement glass you buy now should.
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  13. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Nov 16, 2010]
    Interesting.

    It must activate at a fairly high temperature then, perhaps 10-15c rather than <5c.

    Its also unrelated to the mirror position switch. The power feed goes from the fuse box directly to the glass.
    #12

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