87 5KCSTQ How to shorten afterrun time/battery drain

[Paul Meyers]

This is an idea I got from a lister several years ago and finally got around
to implementing. I'm so happy with it that I wanted to repost it to a
(potentially) new crop of Audi fans.

The typical application is a commute home on the freeway on a hot day with
the AC on full. On exiting to take city streets (read stop and go traffic)
to get home, the temperature rises dramatically. You pull in the driveway
and the afterrun system comes on and stays on for what seems like a half
hour, depleting battery charge and maybe even requiring a preventative
battery charging once a week to keep the charge up, especially if you do a
lot of short trips in hot weather.

Solution: install a manual switch on the dashboard to turn the cooling fan
to "hurricaine mode" when exiting the freeway, so that, by the time you get
home, the engine is cooled down to the normal temperature range.

The 3rd stage fan relay is under the instrument panel. This provides easy
access to implement a manual switch that allows the driver to decide when to
turn on the cooling fan to "dump heat" from the cooling system.

Any 12V single pull single throw panel-mount switch will work. You might
want a reasonably attractive one if you install it in a rather visible
location. I installed mine under the leftmost AC vent on the dashboard
(directly to the left of the auxiliary relay panel access door) for easy
access but still a relatively unobtrusive location. I used a rectangular
plastic affair thoughtfully provided by Blau with my last eurolight wiring
harness. It remained unused, since I wired the H3s to come on with the
brights.

The 3rd stage relay has some rather beefy wires running to it, but you don't
need to access them. I put a tap (commonly used by alarm and radio
installers - I got mine at Pep Boys) into the green wire supplying the 12V
signal to trigger the relay and ran the resulting signal line to one side of
the switch. I found a source of 12V in a common red connector with several
spare connections with protruding spade lugs pretty much directly under the
center of the instrument cluster. I simply attached a female spade lug to a
supply wire, attached one end to the 12V source and the other end to the
other terminal of the switch. Voila, instant control of the 3rd stage fan.
No muss, no fuss. Since the switch was rectangular plastic and is held in
place by tabs at either end, I drilled two appropriately sized holes and
shaped the resulting oval into a rectangle with a wood rasp. After pushing
the switch into its new rectangular home, the result was a tidy installation
that is flush with the panel but easy to find.

Properly used, manually initiated cooling will allow the afterrun system to
come on only in extreme situations, when you really need it, rather than
every time you use the car in hot weather.


Paul Meyers
'88 5KCSTQ Pearl, 128K Mi, 2pc EM, Fuchs, K24, 1.8 bar, Bilsteins
'87 5KCSTQ Gray, 154K Mi, Fuchs, SJM chip, 1.8 bar, Boges
'87 5KCSTQA White, 208K Mi, Replica TT wheels, Adjustable WG, 1.8 bar,
Bilsteins, no roof rack