Need new channel balancers

Thanks for posting. This looks like an S395-33. You have to choose a stamp option for the replacement balances. The stamp designates their strength of the balance. For any balances stamped 32-2, you can use a stamp option of 3220, which supports a window sash in the weight range of 13 through 18 lbs. However, for balances stamped 32-9, that stamp is from an obsolete rating system we do not use. Are these balances from the same window, or separate ones? If they're from the same window, then the 3220 stamp may work for both replacements. In either case, we advise weighing the window sash. You can match that exact with one of the weight ranges listed alongside each stamp option under the product description of the S395-33 page. Let me know if you have further questions. 

Yes, if the window weighs 20 pounds, 3230 would be the correct stamp option, as this designates a balance that will support a weight range of 18 through 23 pounds. Did you ever have trouble opening or keeping this window open prior to the balances breaking? If so, that would certainly be a sign that the original balances were too weak for the sash weight. It's also possible the original owner just swapped out broken balances with incorrect strengths, as you surmise. Either way, let me know if you have further questions.