Re: Outside temperature readout

[steveb@newkla.kla.com]

I am assuming that the V8Q is similar to the 5000/100/200.  If that is true, 
the fact is that there are actually two temperature sensors, one near the 
front grille, and the other in the HAVC shelf (I never know what to call 
the crazy thing!).  The C/C head reads both and makes a decision about the 
temp based on the input.  As I recall there are individual C/C diagnostic 
channels for each sensor, and you should be able to find out if one or both 
are bad.  I think that someone posted their experience with finding a repla-
cement thermistor, and I think we're talking about a couple $ replacement 
part.  I remember giving the person the codes ... let me see if I have them 
in my archives ... yes, it was Fred L. DeRoos.  Here is a copy of a message 
that was posted to the quattro list in April 1995 ...

> From quattro-owner@coimbra.ans.net Mon Apr 24 09:12:32 1995
> Subject: Temp Sensor Info
>  
> Several months ago one of the outside temperature sensors (part of
> the heating/AC system) on my 1990 200Q failed.  The symptoms were an
> outside temperature indication that was always about 12 degrees lower
> than the true temperature.  I compared the resistance of the two 
> sensors at ambient temperature and found that the thermistor under
> the window read approximately 1000 ohms at 25 degrees C, while the
> front thermistor behind the grill read almost 1800 ohms at 25 deg C.
> Since these are negative temp coefficient thermistors and the control
> module always displays the temp of the coolest sensor, it was obvious
> that the grill sensor was defective.  A quick call to Audi and I found 
> that they would sell me a new one for only $95 + tax.  Being frugal,
> I characterized the temp -resistance relationship of the control module and of 
> the working thermistor.  Steve Buchholz also provided  me with the temp - 
> resistance values from the Bently and they matched what I
> measured.  Bottom line is that I  found a thermitor from Digikey for
> approximately $2.00 that  replaces the Audi thermistor.  I  installed
> it this weekend and it works perfectly.  If anyone  has this problem, drop me 
> a line and I'll describe how to replace it.  The new thermistor mounts into 
> the old thermistor housing.
> 
> Fred L. DeRoos
> 
... boy, it sounds like the exact problem you describe!  As far as I know, 
Fred's address is <flderoos@mmm.com>, you might want to try dropping him a 
line ... Thanks Fred!

Steve Buchholz
s_buchho@kla.com
San Jose, CA (USA)