electrical charging problem-Who done it?-We have a winner

[Eric_R_Kissell at email.whirlpool.com]

See below for the winning reply to my question about what part I changed to
solve the intermittent electrical problem with my 1989 200q Avant. James
Marriott responded showing he had identified the flaw in my troubleshooting
logic. I realized my mistake when my wife called Monday to tell me the
problem had returned. Here in the Southwestern tip of Indiana last Monday
was humid and above 85 deg F for the first time this year. Due to the warm
weather, I knew that my 8.5 months pregnant wife was using the air
conditioning and I put 2 & 2 together. You may recall that the AC was the
only accessory we left running for any extent of time the last time we
experienced the problem.

The culprit: a bad radiator cooling fan.

Of course the radiator cooling fan runs constantly when the AC is running, and
it appears that the bearings in the fan were pretty much gone. It would still
turn, but I could push on the blade back towards the motor and rock the blade
tips half of an inch. Somehow this bad fan was pulling enough current to get
ahead of the alternator without melting the fan wiring or 80 Amp fuse in the fan
circuit. Maybe I should have used a 60 or 70 Amp fuse. Another several days and
the fan would likely have seized. I still do not know if the alternator should
be able to keep up with the electrical requirements of the engine plus a bad
radiator fan pulling some serious current. I was lucky enough to find a radiator
fan in the u-pull-it that looked to have been a recent addition to the wrecked
car prior to joining the salvage yard. Seven blades and all => $14.

Thanks for playing,

Eric Kissell

______________________________ Reply Separator _________________________________
Subject: Re: electrical charging problem solved - Who done it?
Author:  <James at ringsperformance.com> at INTERNET
Date:    4/16/2002 9:00 PM

> I reasoned that the AC compressor should not hinder the
> performance of the alternator because it is driven from the crankshaft
> with its own pulley.

However, Audi was smarter than you (and nearly every other car maker), and
makes the fan run on "low" any time the climate control is engaged on any
setting but "econ." Even at 0 deg (compressor won't run anyway), key on with
the engine off. Sadly, at highway speeds the airflow through the condenser
is probably plenty for AC operation, but the fan runs anyway (at least a DC
brush motor draws less current when it is being "helped" like that).

cu, James Marriott
'84 4kq beater, 217k, for sale (BUY IT!)
'87 4kq (alias "late-B2 90q") with rare ersatz NG engine, 184k
'89 200q (MC1, ProconTen/no bag, 1.8 blah blah), 142k
Boise, ID, USA     http://www.webpak.net/~marriott/
www.ringsperformance.com