Andersen balance 24-939 is not holding up sash.

It's hard to say. Can you tell me what each stamp on the old balances read? That is the best way for us to confirm whether the 24-939 is the proper replacement. There may have been some variance in weight between this window and the other window you mentioned that would require a different strength balance, but the only way to know for sure is to know the stamps on your old one. It may be better if you take pictures of the old stamps; sometimes seeing how they're printed is as important as the stamp itself.

That will definitely make things harder. Give me the height and width of the visible glass for the sash you're having trouble with. We will try to estimate the proper replacement based on that information.