Furnace in attic doubling as AC air handler ?

[GoldDigger]

One reason is that a lot of the newer energy efficient units are using ECMs, Electronically Commutated Motors, that are essentially like having a VFD and motor in one unit. So what voltage you give it is less relevant now because all it does is internally rectify it to DC first anyway.

A very good point, especially given that many units, even before ECM, had provisions for different blower speeds for heating versus cooling.