Help Me Preserve My Repurtation

[Huw Powell]

> Paul, did you figure out why the fan was kicking in at
> such low speed, which as you said was much lower than
> the normal low speed fan, as controlled by the fan
> switch?

Good question.

> Two years ago, I had a similar incident in my VW QSW
> and was quite possible the culprit in your daughter’s
> car.
> 
> The culprit: Loose fan wires at the fan switch
> connection on the radiator. A loose connection of the
> wires to the fan itself would also cause the same
> problem. 

The latter, perhaps, but not the former...

> Back then, upon popping the hood of my car, a
> burning-wire smell emanated right from under the
> radiator where the fan switch is located.
> 
> Power was being supplied still but because the
> connection was very loose, the fan turned very slow
> and the connection at the fan switch was overheating
> because of power overload. 

Your car, and any and all Audis since I can remember, have a radiator 
fan relay.  The switch itself only triggers the relay, the relay handles 
the high current of the fan motor.

> As I pulled the wires off the fan switch, a little
> flame lit up, destroying both, the female spades and
> its plastic casing.

Yipes.  What are the odds that someone bypassed the relay on your car at 
some point?

> Fellow listers, please correct me if I'm wrong on this
> one.
> 
> Here is what I think:
> 
> I believe the two hot wires connected to the fan
> switch in my QSW (same as in the 5KTQ) carry the same
> amount of power to the fan.

It's not the same as the 5ktq, but anyway, see comment above re: relay.

> A resistor regulates (located on the fan bracket in my
> car) the power on one of the wires to run at lower
> speed, which equates to the lower temperature setting
> on the fan switch.

On the QSW/4kq/cgt, the resistive drop is only used for the afterrun fan 
triggered by the sender on the back of the head.

The type 89 cars (as I think the subject car was) have a double switch 
at the radiator and two distinct fan speeds, relay controlled, using 
three wires to the fan motor.

It *could* be that the problem car was running on the slow speed, and it 
was unfamiliar to the owner?

> Then second hot wire does not have a resistor hooked
> up to it, thus, full power is applied to the fan.

> By the same token, I think a failing resistor would
> cause high fan speed to kick in at the lower
> temperature setting on the fan switch. 

In the circuit you describe, no, it wouldn't.

One "problem" with the two temperature radiator fan sender is that if 
one part dies, the owner won't really know - when the second one goes, 
that's when you realize you have no radiator fan.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/