On 2016-10-08, wrote:
On 8 Oct 2016 04:09:34 GMT, "DoN. Nichols"
wrote:

3-speed fan motors depend on the load of the fan blades or
squirrel cage fighting the input current modified by the number of turns
in the selected winding. In your application, it would likely run close
to full speed on all three windings.

The multispeed blower motor on my old furnace switched the number of
poles and the speed difference with no load was VERY noticeable. The
torque was almost the same at either speed - resulting in a large
difference in horsepower as well.

O.K. Quite different from mine, which has a squirrel-cage blower
and a motor with two windings -- a cap shifted one for starting and run
torque, and a multi-tap one for various speeds connected directly to the
power line. Change the tap, you change the speed when the squirrel-cage
is present, but for an unloaded motor, the speed does not noticeably
change (and is *much* faster than any of the speeds with the cage
present.)

Perhaps the vintage of the furnace involved. Mine is a Carrier
from about the mid 1990s when the house was expanded.

Enjoy,
DoN.

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