Are the seeds you are seeing fully developed? If they are, something is pollinating them early in flower. Your flush is usually in the last couple weeks so that should not be the cause because the seeds wont have time to develop. Any kind of light leaks can trigger a hermie. Now whether or not the light from the ac is powerful enough I have no clue. I usually do like you did and cover it with something. The ac that i use was actually letting in light through the vents from outside. I had to install an awning that kept the sunlight off of it outside. Easy fix that worked wonders. If i were you, id sit in the flower room with lights out for about 15 minutes and make sure there are not any light leaks. Just something you might wanna check out. Could be an easy solution. Could also be pollen from one of the males given the amount of seeds you are talking about. It only takes a little pollen to screw up a lot.