Rad Fan intermittant - killing the battery

[SJ]

Problem summary:
88 5k non-turbo
Battery goes dead because the radiator fan turns itself on intermittantly
...with engine stone cold.


----- Original Message ----- 
From: "Konstantine Bogach" <kbogach at comcast.net>


> I am facing same problem on UrS4 '93.  More accurately - faced, as after
being intermittent for a while it decided to run constantly (without
ignition on).
> It turned out to be after-run relay.
**** Thats the conclusion I came up with. There is no other source of
controlling voltage to the motor except thru the after-run relay.


>It is actually control modue as there there is no coil and contacts inside.
Same unit is used in 200tq and UrS4 '92-93.  I am not sure what is after-run
schema in your car.
****I took the cover off the relays in both my cars. Inside there is a
circuit board and a mechanical relay. The part number is 443 955 532C
I tried to locate the part in the FA. It does not show up in the parts list
for the relay panels. However, when I do a "where used" I get a long list of
car models where the part is used.
My local audi parts guy can get the part for $35.


>SJM site describes this problem and shows picture of the module on UrS4.
200tq has it under driver's kick panel, >UrS4 under passanger's kick panel.
Damn thing is dealer only and costs $112.  SJM mentions that resistor or
>transistor gets burnt but there are too many of them there.
****You have the all electronic version - no mechanical relay. They must use
a thyrister or transistor to act as a current switch.
I think the problem is due to bad electrolytic caps. They tend to dry out
with age. In some circuits, they will lose their "form" because of the low
voltages used. At that point, they act crazy. The caps will work when cold,
but not when warm. That appears to be my symptom. With the warm weather, the
relay is not acting up.

> Initially, when debugging the problem I went crazy because it ran with
everything on the diagram disconnected (2 >relays and rad switch) but it
turned out that the diagram in Bentley does not have after-run system in it,
for UrS4 at >least.
****Easy to troubleshoot when its bad all the time. Mine acts up only
sometimes . .. always in the middle of the night when I'm sleeping. All I
find in the morning is a half dead or dead battery.
The manual doesnt have much theory on the topic. From what I can gather, the
after-run relay has a timer that is started when you switch off the
ignition. The timer runs for 10 minutes, then shuts off. As long as the
timer is on, the relay module will accept the open/short signal from the
underhood temp sensor and the relay will turn on the fan.
After 10 minutes, the relay shuts down and will not react to inputs from the
sensor.

Today, I swapped relays from the 5000 to the 100. The 100 has the relay in
the main fuse box. Thats a lot easier to get at than the auxiliary panel in
the 5000.
I'll stop at the local junkyard and see if I can pick up a couple of these
relays and swap out the bad one in the 100.


SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q