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89 100 alternator or a/c fan problem

Hi Everybody,

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
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
replaced the whole alternator with the bosch rebuilt and it seemed to
even though I still thought the voltage was too low when the fan kicked

Any Ideas ?

I'm leaning towards fan problem, but I'm not sure what too check to
it ?

Thanks Everybody :-)

Mike L.
90 V8
89 100 Wagon......... currently not running a/c even though it's 90+ ;-(