2001 sienna blower motor issues

Trying to work on my moms van 2001 sienna, front ac and heat works, the rea does not. Im gunna check fuses. What is throwing me is my mom says she shuts off all air, and just turns on the rear blower motor and no air comes out of rear vents, but she says she can hear air blowing under the dash.

Is there vents that go from the rear blower to the front that could've gotten unhooked?

What r the chances its a fuse?

Is this a common enough problem that it will b an easy fix or am i biting off more than i care to chew