nothing found. don't even understand how to replace.

Thanks for posting. This is a Coil Balance system. Coil Balances are spring mechanisms that enable the opening and closing of your window sash, or the movable part of the window with the glass. The bottom part that connects to the window sash is a pivot shoe. In this, your pivot shoe looks like our 15-087. The identity of the pivot shoe determines the kind of coil springs you have, so we know based off your pivot shoe that your window uses Series 180 Coil Springs. You will need to look for numbered stamps on the coil springs to determine the spring weights you need for each spring. If there are no numbers, or you are confused, please weigh your window sash on a bathroom scale. We can then use that exact weight to work out what spring weights you need. 

For removal and replacement details, see the video below.