Window sash won't close after replacing the window balances

It sounds like you may not have the correct length. I see you ordered the 24" Series 395 balance. What is the length of your old balance's metal channel?

I think that's the problem. The number on the metal channel is not a direct match to the actual length. In fact, with a stamp of 2430, the length of the metal channel should be 25". I know that may seem confusing, but keep in mind the stamp has more to do with the strength of the balance than its actual size. When determining the size, it is important that you measure it to confirm exactly what length you need.