You are using the forward and reverse buttons on the RepG control panel to test this, right? if you don't hear at least a whirring noise or a click then it's likely there's a problem with either the stepper motor itself, the cabling, or the stepper controller board. In my experience cabling is always the first suspect. Not sure about the fan speed thing, on my ToM the fan comes on when the extruder hits 50 deg C and then stays on.
Seems to me the first thing to do is test the stepper motors and controller boards. Since the MK7 and Y (and X) axes use the same motors, cables, and boards, it should be easy enough to swap the motor cables between the A axis and the Y axis and see if the problem follows the motor/cable or the board. You don't need to physically move the motors, you're just interested in seeing if they step or not. Note: BE SURE TO TURN OFF THE POWER AND UNPLUG BEFORE SWAPPING ANY OF THESE CABLES, bad stuff can happen if they are pulled when powered up.
if the problem follows the motor/cable, then shut off power, swap the cables only, and see if the problem follows. if the stepper motor still doesn't turn, it's probably bad. In any case, once you've done this you should be able to contact MakerBot's excellent support team knowing what doesn't work; they will most likely be happy to replace the non-working part for you.
