On Wednesday, June 4, 2014 11:22:24 PM UTC-4, wrote:
My experience is that the motors fail if they are used in ducts with hot air. The thermal protections cut out.



I would set the air handler blower in the furnace to a higher setting.



Mark

If you have that option, in many cases you don't, particularly for
cooling. The older blower motors used the highest speed for cooling
to begin with. The newer ECM motors may have a higher speed setting,
it's certainly worth checking. But even that may not help, because
you're just moving the air around faster, not changing the relative
proportions. Move enough air downstairs to get the thermostat to turn
off and it still turns off, leaving the upstairs probably just as hot.
What is really needed is to get less air downstairs, more upstairs.
Shutting off some downstairs registers in areas that get cold first
can help. You just don't want to cut down the airflow too much by
closing too many.

A lot of this could be solved for little upfront cost when it was
installed. What should work would be a dual stage compressor, an
automatic damping system, and an additional thermostat for upstairs.
If the lower level is cooling off and nearing the desired temp,
the unit could switch to low stage and put most of the air upstairs.
Doesn't seem like anyone does that though. More common and expensive
solution is to use two furnace/AC systems. That brings it's own
problems, because the second system winds up in the attic.