HVAC Issue

[tonyt102]

Hi all.

Been away from the forum for a while. Sold my last S8 of 4 years about a year ago in favor of a newer B6 A6 S-Line Avant 3.0TDI... big mistake. Not sure what it was but I just haven't gelled. Anyway, after a year of looking, I've just bagged myself a rally good Final Edition however, I have a HVAC issue.

Here are the symptoms:

On my way home, there was a constant hot air to the foot well which couldn't be turned off although this hasn't happened since.

Auto function is intermittent. Even when it appears to work, warm(ish) air comes through the foot well but the center vents and screen vents blow cold air. Sometimes when I press auto, the blower stays on one bar and doesn't do anything.

I've read several threads some suggesting that maybe the control unit itself maybe at fault. When I first bought the car I did a full scan and there wasn't any codes present. I've since done a calibration and scan and it's shown up the following codes:

00728 - Potentiometer in Positioning Motor for Left-Hand Central Vent (G136)
09-00 - Adaptation Limit Surpassed
00734 - Potentiometer in Central Vent (G142)
30-00 - Open or Short to Plus



Not sure if it's got anything to do with it but the engine temp doesn't seem to run as high as my previous S8, it never really gets to 90, more like 75/80ish. I've got a feeling it's the thermostat but any other suggestions would be appreciated.

Cheers.