Comparators Dragging Each Other Down
The LM393 has open collector outputs. That means they can pull down, but not pull up (That's probably why you need the pull-up R16). 

The open collector output means you can produce a wired AND connection by tying two outputs together. You can't create a wired OR with typical comparators. You will need some kind of added gate or a couple of transistors to create the OR function you want.

If you want to create the OR function using diodes, you will need a separate pull-up for each of the two comparator's outputs.