stevepaa

Can someone expalin what the reistor does and how can a siezed blower catch fire?

botoo

The resistor part of the item is in the airflow downstream of the blower, and it can get very hot. If the blower is not working or seized, the airflow does not cool the resistor. The new resistor part has a circuit breaker built in to limit the temperature, I assume.

I just checked my resistor and the part number is clearly stamped on it. If it ends in a 2, it should be the new part. My resistor had fallen out of the duct so that is also something to check.

robbed666

Its not just the airflow. With a DC motor of this type, when stalled the current is only limited by the armature resistance, which is very small. So the resistor has just about the full supply (12-14Volts) across it. This causes several tens of amps to flow, instead of the few in normal operation. You end up with a 'bar fire' in your plastic blower housing!!

stevepaa

Help me understand this better. What is the purpose of the resistor?

robbed666

Basically the resistor is switched in and out of circuit by a relay controlled by the heating control module. The resistor's purpose is a crude form of speed control of the fan motor. When switched in, the resistor reduces the voltage to motor by introucing an element that when a current is passed through it, a potential difference is developed across it (a Voltage drop). Therefore there is less voltage across the motor terminals, and with a given load on the motor, the motor will slow. This is a very simplistic view, but should give you the idea.

stevepaa

So instead of really using a step down voltage transformer, they use this in series with the motor? Aaagh.

robbed666

You can't use a transfomer on DC ! A better idea would have been the offset brush method employed in two speed windscreen (windsield U.S) wiper motors. Or even PWM, bit off an over kill though! Who knows where they dug the motor up from, I doubt it was designed from the 'ground up' for the blower motor in a 964.

I'll replace mine with one of these with a thermal cut out bolted to the chassis. Another job the list goes on!

MARC A. 964 C4

Tinwan,..
So many things are put into the right perspective after having looked at those photographs. They have brought me back from the clouds and planted me on level ground again. To those that are educating me, "I thank you"... To this heart broken Man and his Wife I can only send you my, "Best of Luck for the future"... I’m so sorry this happened to you... Good luck with the repairs and in due time you’ll be back on the road again... Hang in there...

From France,
Marc...

Crivens

crikey.
i put my 964 engine in my 3.2 I dont think I bothered with the resistor

www.red964.com/html/dyndex.php
www.projectsonly.co.uk

GT9111

Can someone show me where this resistor is located?

Computamedic

I can't show you - but if you put your left hand between the engine compartment electric panel and the pipe coming out of the rear blower you should be able to feel for two wires apparently attached to the blower pipe. Those two wires are spade connectors which attach to the resistor in question. The resistor itself is snapped into the blower pipe and can be removed with a little effort and conviction.

Hope that helps. If you NEED a photo I can take one later.

Regards

Dave

Tinwan

Hi all,
Most would be pleased to know the unfortunate C4 cab will back on the road soon. Still a hell of a lot of work to do although lucky this fire was out in about 60 seconds so imagine if was any longer. This engine was stone cold & not usually associated with the blower & or resistor hot engine (problem) as the resistor was changed (factory recall) very recently so check your fuel injector rails and lines for any leaks I guess.
Cheers, Mark

tafkai

hey mark !!

i was only thinking about you earlier today !!
i guy on german ebay has wiring harnesses for sale .

Tinwan

Hi Ian,
Thanks, They were able to buy all the parts they needed in the US. They wanted to complete the car nearly all at once, the roof that can also be fixed locally. The paint will be done next week and the reconstruction the week after. They will replace some other essentials on the engine before she goes back together.
Cheers, Mark

Tinwan

Hi all,
For anyone interested, the fire damage restoration continues , engine & gearbox back together with new clutch & flywheel in next week.
Cheers, Mark