The heat-sink would need to be enormous for that to happen.

The size of a light bulb I think.

 

The heat they produce is too much in an enclosed space and they would burn out in no time, you would not want to touch one on fan speed one.

I don't know exactly how much power the fan motor consumes, but I think that figure is close to 100 Watts at full power. Assuming that on speed one it consumes ¼ of full power, the resistor dissipates equal 25 Watts, only 4 Watts more than a P21W bulb.

Edited 10 August, 201510 yr by briskycat

I don't know exactly how much power the fan motor consumes, but I think that figure is close to 100 Watts at full power. Assuming that on speed one it consumes ¼ of full power, the resistor dissipates equal 25 Watts, only 4 Watts more than a P21W bulb.

75 watts dissipated I think you'll find, leaving 25 for the motor and it's not producing light it's producing heat.

75 watts dissipated I think you'll find, leaving 25 for the motor.

I assume the motor and the resistor are connected in sequence. That way I don't see how the resistor can possibly dissipate 75 Watts. 25 Watts is the maximum for that arrangement if my calculations are correct.

 

and it's not producing light it's producing heat

Incandescent light bulbs also mostly produce heat, not light

I assume the motor and the resistor are connected in sequence. That way I don't see how the resistor can possibly dissipate 75 Watts. 25 Watts is the maximum for that arrangement if my calculations are correct.

Incandescent light bulbs also mostly produce heat, not light

I don't know why I bother.

Nothing going thru resistor Motor at full speed say 100w

Resistor dissipating 25w leaving Motor at ¾ speed using 75w

Resistor dissipating 50w leaving motor ½ speed using 50w

Resistor dissipating 75w leaving motor at ¼ speed using 25w

Not exact but not too far out.

Try holding the wound elements of the resistor for a few seconds on ¼ speed.

Edited 10 August, 201510 yr by Urrell

Here is my version:

 

X is the speed (desired power over the nominal power of the motor)

Y is the power that the resistor dissipates, relative to the nominal power of the motor.

Edited 10 August, 201510 yr by briskycat

I think the resistor pack is wired in parallel with the motor acting as a variable shunt so the dissipation would be constant.

 

Fred 

Usually the wiring looks like this:



http://www.resistorguide.com/applications/blower-resistor/

I had a similar problem on my Yeti - lights on the unit, flaps moving, no blow. Changed the control unit in the dash. It worked for about a month and happened again. Local independent pulled the system apart and found that if they fed power direct to the blower motor it worked fine. The problem turned out to be a ten way wiring connector somewhere in the system, although only four are used. At a cursory glance it seemed OK, but with a more careful look you can see that the connectors have burnt out. For a unit that has to carry up to 40 amps, its looks totally inadequate. Cheap part, expensive fix.

 

Andy

Usually the wiring looks like this:

http://www.resistorguide.com/applications/blower-resistor/

 

The mk1 fabia implementation is just like that, and judging by the similarity in appearance between the yeti part and the fabia one, I'd say the windings are identical, so I'd expect the yeti circuit to be the same.

One could measure the three series resistances (leftmost device is a thermal fuse), measure currents by putting an ammeter in place instead of the fusebox fuse and then do I²R calculations of dissipation in each switch position if really interested.  If I get really short of things to do one day, I might.

 

Usually the wiring looks like this:

http://www.resistorguide.com/applications/blower-resistor/

I stand corrected it is in series.

 

Fred

My heater fan has failed twice.

On both occasions speeds 1, 2 & 3 did not work, but 4 was OK.

I was told that speeds 1, 2 & 3 were controlled by a variable resistor which had failed.

Speed 4 by-passes the resistor to run on full power, hence why it still worked.

On the first occasion (this summer) just the resistor was replaced. 

On the second occasion (to-day) the resistor was replaced, but the wiring to the resistor was inspected. 

Skoda (I assume) have issued some sort of directive regarding these failures.

The wiring was found to be chaffed and presumably shorted on the bodywork.

I hope that this has cured the problem, as my Yeti is out of warranty in the new year.

 

Now that it has failed for the third time they are now saying that no wiring was replaced on the second occasion, just a new resistor?

 

As my Yeti is out of warranty (only 3 years) I will have to pay for all parts and labour.

 

Should I get some sort of warranty on the failed repairs?

 

The blocked pollen filter theory sounds interesting as the resistor always fails in the summer.

No warranty on the failed repairs :-(

 

They wanted £84.00 to fit a new resistor !!!!

 

£7.99 on ebay and five minutes in the passenger side well.

 

Job done.

 

Thanks to Urrell for the links to the YouTube clips.

 

Tony

 

£7.99 on ebay and five minutes in the passenger side well.

 

The eBay ones tend to smell for a day or two but that's OK this time of year when the windows can be left open when driving and on speed 1 will smell the most but clear it quickest.