[Biturbos4] Lack of heat in B5 series car - any thoughts?

[mkb]

>>>>>>>>
The climate control head should be scannable with VAG-COM.  If there's
 a
stepper motor failure, it'll surely turn up there.  And that's where
 you
should start the diagnosis.

When he changes the cabin air filter, it would be a good opportunity to
check for debris (leaves, dead rats) as well.

Mark Rosenkrantz
('87 4KCSQ, '00 S4, and a bunch of other toys)
On Dec 24, 2007 9:10 AM, Grant Lenahan <glenahan at vfemail.net> wrote:

> OK, its a Passat. and it isn't even mine.
>
> But a friend, who's a pretty fair mechanic, just bought a 2001 Passat
> for his son.  It should be very similar to B5 A4s and S4s in this
> regard, I assume.
>
> One problem is that the heat doesn't work - it blows stone cold air
> (I'm told).  They know the history of the car, and the owner says it
> was working normally one day, and totally gone the next. We suspect a
> mixture (cold/warm air) stepper motor died or a connection to it has
> a problem.  But i've not heard many complaints about this.
>
> Any wisdom? Common problems?  Things to check? Warnings?
>
> Thanks much,
>
> Grant
>
> ps: apologies if this arrived twice. It got caught in moderator
> approval land and never emerged - or not so I saw.
> _______________________________________________
> Biturbos4 mailing list
> Biturbos4 at www.audifans.com
> http://www.audifans.com/mailman/listinfo/biturbos4
>

<<<<<<<<<<<<<

I've had similar problems from day one on my 97 A4 18tqa.  Never bothered to diagnose it until I got p**** off at being cold in the winter.  I did the following:

T-stat was good because I had changed a few months earlier
Changed HVAC head with a used unit (should not have done so until after I flushed the heater core.  The old unit was good)
Flushed heater core a couple times
Checked the hoses to/from the core (both hot which I believe means my heater core is not blocked; also noticed flow from both inlet and outlet when flushing)

I think flushing the heater core helped.  I did this twice.  The first time I did this, I got fairly good heat.  The next day, it went to cold again.  So I did it again the following week.  Made no difference.  I hooked up VAG-COM and got no error codes.  Even accessed the HVAC codes using this fine article (http://www.audiworld.com/tech/int6.shtml).  No errors reported from the HVAC unit.  I can hear all the flaps move.  I can see the flap arms (read and blue) move if I look at them from underneath the passenger seat dash (you should see them move as you increase/decrease temps).  

Weird thing is that after I ran through all the codes from the HVAC unit, it started blowing warm air.  It's now reasonably warm for me and has been for the past 4 weeks or so.  I don't know why (perhaps the Audi gods are being kind to me and letting me have a warm winter in my A4).  I suspect that something is getting blocked or some flap is not moving freely (even though I hear all flaps move).  At some point, when the weather warms up, I might drop the glove box and see if all the flaps move freely.

But I would check the flaps first.  Do you hear them move as you increase/decrease the temperature.  I would then check the in/out hoses from the heater core.  After the car warms up, the in should be hot (furthest from battery in my car) and I think the out should be fairly hot (indicating flow, closest to battery).  Those should be easy to check.  VAG-COM and access the HVAC head codes, again easy checks.

--
mohammed
97 A4 18tqa




      ____________________________________________________________________________________
Be a better friend, newshound, and 
know-it-all with Yahoo! Mobile.  Try it now.  http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ