Re: 89 100 alternator or a/c fan problem

[DeWitt Harrison <de@aztek-eng.com>]

On Fri, 18 Jul 1997 12:08:23 -0400, Mike LaRosa wrote:

>Got a problem with the wife's 89 100 Wagon 116k miles.  When we cruise
>in the city for 4 day's with the a/c blaring.  It will eventually kill 
>the battery.
>
>I've had the battery load tested and it came out ok, batteries about a 
>year old.  The alternator will fully charge the battery if I leave the
>a/c off for 20 minutes or so of highway driving.
>
>I do notice though when the a/c is not running the voltage guage is
>about 13 + volts.  When the a/c is on and the fan kick's in it 
>immediately drops to 12 volts flat.
>
>Is this a problem with the alternator not being powerfull enough to 
>keep up with the draw from the fan or is the fan drawing more current 
>than it is supposed to ?  I seem to remember reading about a similar
>problem before with the fan on the list.
>
>The alternator was replaced last year with a bosch rebuilt for what was
>essentially the same problem.  But at that time I had replaced the
>voltage regulator part of the alternator and the alternator was still not
>putting out enough power to charge the battery when the a/c was
>running in city.  So I replaced the whole alternator with the bosch rebuilt
>and it seemed to
>work even though I still thought the voltage was too low when the fan
>kicked in.
>
>Any Ideas ?
>
>I'm leaning towards fan problem, but I'm not sure what too check to
>confirm it ?

Whoever solves this one will earn the eternal gratitude of many. I
think the most likely answer is that Bosch rebuilt alternators are pure
crap. After my original 90 amp unit died at 90 K miles, I've had
4 rebuilts, none of which has ever been able to keep the battery
charged in hot weather. I have made numerous current draw
measurements and have never observed it to be in excess of 50
to 55 A with all A/C and fan loads on. Yet the voltage at the alternator
fades away in the heat. BTW, once the battery is recharged, starting
and all electrical functions are peachy keen.

One possibility is that the hard working alternator heats up to the
point where the voltage regulator is affected.  I'm not far from
completing an experiment to try a remote or external voltage
regulator. I'm also making resistance measurements in the charging
and other high current wiring (looking good) and redoing the major
ground strap connections.

If an external regulator fixes this, then either Bosch or Audi has
some 'splainin' to do. Other ideas are most welcome.

DeWitt Harrison     de@aztek-eng.com
Boulder, CO
88 5kcstq