People often find that old guillotine windows have to be propped up with sticks and the like to keep them open in the summer, because the counter weight sash cord has broken.
Jon went through the process of how to open up the hidden cavity where the weights move up and down. There is always a trap door on the inner frame towards the bottom of the lower window slide. Look for the painted screw right in the middle of the slide about six inches up from the bottom. The entrance way is a beveled piece of wood that can be pried out. Then replace the cords and assure that the upper pulley wheel is free to turn.
Obviously these large holes in the wall and window frame are not conducive to energy conservation or the elimination of drafts. You may want to seek out special window torsion springs that can be installed on these windows, right in the slide track. It is a bit of work but that would allow you to insulate and seal off the large cavities in the framework.