Radiator fan fun

[Igor Kessel <e6941tb@ix.netcom.com>]

Daniel Lamb wrote:
> 
> Help needed!
> 
> I am a new owner of an '85 5000S that has some quirks.  If anyone can help
> perform an exorcism on my radiator fan, I would be thrilled.
> 
> Basically it turns on or off at will.  I have replace the thermo switch
> (mounted on the radiator) and the thermostat (valve) but the problem
> persists.  Last week on a long trip from Upstate NY to Washington, DC the
> fan went on while I was stuck in traffic but would not go off after over 30
> minutes of freeway (70 mph) driving.  In fact, the only way I could get it
> to shut off was to disconnect the hot wire on the back of the fan.  I
> pulled the fuse and relay, disconnected the thermo switch and the
> temperature sensor (mounted on the back of the cylinder head) but it just
> kept running.
> 
> Finally, on its own accord, it shut off.


Rad Fan Relay No 10, III stage, 40a. It has welded it's contacts closed. Typical.
Replace with the new one rated @ 70a. There has been a relevant TSB issued by AoA.
Your car has 3 fan stages and therefore has 3 fan relays. You probably have replaced 
the wrong one.

> Other symptoms that may be related to this problem are a dashboard
> temperature gauge that runs erratically

4-wire Temp Sender has gone south. Located on the underside of the Al nipple, that 
houses the upper rad hose. Sender is ~$60, new version, has only 3 wires.

> and a heater that blows cold air half the time.

You've got oil in the valves of the A/C controller and/or the tiny electric motor in 
that controler has worn it's plastic gear. In any event, pull the controller (it's 
behind the glove compartment). Once you've fixed the controller, install a gasoline 
filter in-line in the main vacuum supply. Check the archive @ 1-2 weeks ago for 
detailed discussion.

> I believe this is a two speed fan (right?), but I have
> only witnesses it running a one seemingly high speed.
>
> Daniel Lamb
> '85 5000s

Actually it is a 3-speed fan, hence it has two ballast resistors in series.
The II stage fan resistor is blown, therefore cutting out both 1st and 2nd speeds. 
Also typical. The resistor is located right on the front longitudinal member directly 
in front of the radiator. The resistor is a 20cm long anodised Al angle (might be 
either yellow, blue or red) and has 3 heavy wires coming out. Disconect the wires and 
check the resistance between posts 1 & 2, 
2 & 3. Each is ~ 0.7 ohm. If infinity - that section is blown.

Jeez, Daniel, you have just brought back the not-so-nostalgic memories of my long 
gone '85 5000s. :)

Wellcome to the group and good luck.

-- 
Igor Kessel
'89 200TQ - 18psi (TAP)
'98 A4TQ - on order...again. For the third time and counting.
Philadelphia, PA
USA