Pre-facelift door mirrors-heated all the time?

[Nessy]

Thought this would happen at some stage, think one of my heated door mirrors has failed!
Driving home from work last night (ambient temp 15-16 degrees C according to dash display), typical wet early evening, I noticed that neither of the door mirrors cleared themselves, but I thought on my A4 they were heated whenever the ignition was on (they were on my '94 80 Avant)?
As an experiment I turned the heated rear window on and after a trip of about 5 minutes got out and felt the mirrors, o/s felt warm but n/s was stone cold......
Does this mean the mirrors are heated only when the HRW is on?
Looks like a new mirror glass is needed but would sure like to know when the mirrors are meant to heat up!

Thanks.

 

[Z82]

I was always under the impression it was only when the rear windscreen heater was on.

 

[rasA4]

just as a guide mine is a facelift and in the owners manual states that "The mirror surfaces are heated according to the outside temperature when the ignition is on." does not tell you what the temp should be??

have you checked your manual if you have one?

HTH

 

[Nessy]

Thanks for the replies chaps, having had a search on this forum earlier it seems that early A4's (like the 80) had mirrors heated whenever the ignition was on, consequently they burn out in no-time.
Audi then appeared to change it to a system linked to the rear window so that only when HRW was on would mirrors heat up....have no data when this change occurred but am guessing my late '98 built (early '99 model) car incorporates this feature.
Think the facelift cars have mirrors with a thermostatic switch on the reverse side of the mirror glass (going by some pics I found when doing my afore-mentioned search earlier which show a round sensor-type thing),which causes the glass to heat up when ambient temp is low....
Handbook with my car is for the later facelift model so isn't really any help.....
So, it looks like there are 3 different ways the mirrors can be heated, unless anybody can correct me.....please do if this is wrong!