RE: A/C intermittent?

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> >Beats me.
> 
> >My '95 A6QW does the same thing.
> 
> >I've never been able to get a climate control diagnostic
> >code out of it. Mine doesn't have anything to do with resetting
> >the temp. It just "shuts off" the A/C once in a while. Cycling
> >power to the car always resets it.
> 
> Mine too! This has happened to me half a dozen times. If I can I pull
> over, 
> shut the car off and then start up again, its fine. Although that seems a 
> successful solution, I too would like to get whatever is causing this,
> fixed, 
> while the car is still under warrantee.
> 
... I'm not familiar with the newer cars, so my apologies if this does not
apply.  I've read in the service manual for my V8 that if the system
receives a certain number of excessively high pressure reports (8) from the
refrigerant it will shut off the compressor.  I would imagine that this is
more likely to occur on hot days.  It states that all one needs do is to
turn off the system from the front panel and then turn it back on again to
get the compressor back on.  Here again, on the '91 V8, what happens is that
the system will blink the outside temp light for one minute before shutting
off.  IME it is very easy to not notice this happening on the V8 ... and
have the compressor shut off.  

There is another fault listed that could be related to playing with the temp
setting ... and that is that if the system finds that it is not able to move
the blend doors to the proper position that will create a fault.  I didn't
think that this fault would result in shutting down the compressor, but it
very well might ...

Keep in mind that the HVAC system is likely to lose its memory when you turn
the car off, so the best bet is to alert your service people about the
problem (one to be sure that it was reported while the car was under
warranty) and have them show you how to actuate the diagnostic mode and
determine what the system is reporting when it decides to shut off.  Unless
the clergy has decided it was too easy for the laity to learn the
diagnostics; it should be as easy as pressing a few buttons on the control
head to activate the diagnostic mode.  

HTH!
Steve Buchholz
San Jose, CA (USA)