Can't find limit switch location on norodyne furnace model fg6rc 080c -16b. Updraft gas furnace. The red led stays on solid, works with ac, bit won't run at all for heat. No reset buttons, I found 2 are poped out. I found 2 bad limit switches, L250-25f , laying by the furnace from last service calls for same problem. I can't see where this thing is to replace it! Any help would be appreciated as I'd like to do this myself. Thanks, Lars