For the average old window what is the maximum weight air condition you should have installed without any support brackets beside screwing in the window frame from the inside? For example up to 50 pounds ok? 100 pounds risking it?
100 pounds is nothing for a window frame. Now if you don't have it mounted right you could break, crack or put stress the bottom of the actual window unit. This isn't a question of weight though, it is a question of how balanced it is and movement.
Is a 100 pound vs 50 pound AC unit more likely to have install issues... probably.