S4 B5 Heated mirors..

[s4best4]

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.

 

[Blue_Thunder]

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.

 

[jcb]

mine are always on (99 facelift),

 

[aragorn]

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.

 

[s4best4]

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.

 

[GSB1]

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.

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.

 

[aragorn]

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.

 

[jcb]

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

 

[andybnwc]

Also the mirror adjuster has to be in the centre too i think

 

[GSB1]

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.

The thermostat (sensor or whatever) breaks the circuit, unless it is cold enough, then the circuit completes and the mirror element heats.

 

[GSB1]

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

Exactly. Early glass did not have this, original replacement glass you buy now should.

 

[aragorn]

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.