Just thought this might help somebody in the future:

I've been putting together a new 240 and the power windows were having problems. Cleaning all of the switches made 3 out of 4 work just fine, but the front passenger window was still stuck. I tested the power at the switch and had 12v (engine not running) and strong grounds. I knew the motor was trying to work because I could hear/feel the strain when the switch was applied.

I assumed that the motor simply could not overcome the strain of a rusted or seized mechanism and this was partially true. As it turned out, the mechanism was so jammed against the up-position stop that it could not free itself. Loosening a single Allen screw was enough to unbind the entire mechanism and now the regulator works great.

If you ever find yourself with a seized window regulator, try loosening the stops first.