Does the bottom window spiral balance control both windows? Or is there supposed to be one for the upper window too?
Oh, I see. Yes, the top sash should also have its own spiral balance. It might be the same as the bottom sash, but this is not always the case. I would see if you have an identical window elsewhere in the house that you can use as a reference.
I realized that the spiral balance is not connected (broken?) on the top window. Hadn't noticed this previously. I presume this can be replaced?