how much weight can a lofted bed hold? because i have a son who is
over 300 pounds that is moving into a dorm room in PV Main at ASU and
his going to sleep in a top bunk of a lofted bed. Will a lofted bed
hold his weight?

I don't think there is any way to answer this without knowing more
about the bed in question. Not all beds are constructed in the same
way, and not all beds will have the same maximum capacity.

If this is a university dorm, I suggest that you contact the
university. They may have access to the bed manufacturer's
specifications.

As a recent dorm dweller, I spent quite a bit of time in a bunk! 
Though it is true that maximum loads will vary from bed to bed, I
would say with some confidence that most bunk beds would hold him
without fear of collapse or failure.  However, I would take into
consideration other factors such as the fact that he is going to have
to get into and out of this bed at least once a day.  And I say this
not to be critical or condecending, but I forsee this as being a major
complication: both physically and socially.  If he doesn't know his
roomate or suitmates, getting in and out could definitly create an
akward or embarassing situation, which is definitly not a good thing
for a freshman in college no matter thier size.  I would reccommend
contacting the roomate and trying to negotiate a switch of bunks or if
he/she is unwilling perhaps a room switch through the university.

I lived for two years at ASU in Irish Hall. We had steel bunk beds and
there was no problem with the top bunk simultaneously holding two
150-pound people. If the PV beds are similar, you'll be fine.