530d. Erratic climate control fan

My 2000 530d se has developed a fault with the climate control fan. It now fails to respond to the +/- control and comes on at full speed. Irrespective of the temperature settings it maintains max speed. It
can be switched off with the +/- control.
This looks like a failure in the speed control device? Is there a seperate unit controlling the speed, or is this an integral part of the fan motor assembly?
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Sounds like a fault in the final stage resistor. Try googling for that phrase and all will be revealed!
Roger
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