I wouldn't put a load on the roof of a
Fiber Stream. The air conditioner, when installed, is in the strongest part of the roof between the
fridge cabinet and the little pass-through window wall. These two structures are the only thing that keeps the walls from bulging out due to the forces of the roof. I've seen a few where the screws from the outside going into the wall and
fridge cabinet have decayed, and the walls bulged out significantly. If you've torn a Fiber Stream apart before, you'll know that these walls and cabinets are extremely
light weight, and not attached to the walls very well.
I took the A/C off my roof, but that was also due to a ridiculous installation that involved putting a 4' x 4' piece of plywood on the roof with no sealant below.
Definitely ladder work IMHO.
Randy