window sash springs

I have used the 20-001 springs in the past and to my amazement they do work well for this function. I'm surprised that your sash weights won't support the sash. I would first check to see if the cord or chain attached to the weight is not hanging up inside the window casing. There should be a cut-out to access the weights in the side track of the window frame. Also, if need be try to purchase a heavier sash weight. You can sometimes find them at old Hardware stores or at a scrap yard.