On Mar 23, 6:48*am, Clive wrote:
In message
,
" writes Instead of just a simple
fan motor, it's a fan that's variable speed, driven by a PWM
signal.

If by PWM you mean pulse width modulation, then it would allow for
variable speed, but a DC motor is an inductive load and is not sensibly
controlled by such a system unless there is something in the circuit to
allow the peak voltage generated by the motor at pulse cut of to be
shunted to earth.
--
Clive

That "something" could be as simple as a diode. PWM is
commonly used to vary the power to a motor. BMW, for
example, uses it on the aux fan motor of the X5. And I
would suspect that it's also used for the blower motor
because you wind up wasting a lot less power that way.
And every little bit of power saved adds up and effects MPG.