On 4/28/2015 8:47 PM, Lloyd E. Sponenburgh wrote:

The speed [current?] is dependent upon the mass of air being moved. It's pretty
large when sucking and blowing freely. The motor does the most work
moving the largest volume. When the inlet is blocked, the fan just
recirculates the air in the volute, and it's (essentially) unloaded.
...

Oh, yeah ... I remember now, about the current increasing as restriction
decreases. Seems paradoxical until you think about it as a matter of
mass of air being moved. Thanks for that "model".

Now, back to the original problem: with the "extractor" operational, it
was overheating. The mass-of-air model would suggest that the cause of
that would be an air _leak_, not a blockage. I'll look into that & be back.

Thanks,
Bob