Channel Balance replacement for Nu-Air single hung window

A home owner from Florida says:
I am trying to find replacement balances for my Nu-Air double glazed,single hung window. I had attached Photos of the balance in question. The balances are failing frequently and local supplies have dried up now that Nu-Air is out of business.

The windows are quite heavy being double glazed and the movable sash measuring about 36" by 32". I am not sure the installed balances were up to the stress of the weight since, while they balanced fairly well, they keep breaking; usually at the pulley. What part do you recommend installing to replace the failed balances? Thank you for your help!
A customer submitted photo of channel balance attachments.
Profile picture of Paul
Paul from SWISCO responded:
Thank you for posting in our discussion board. Before I can offer any suggestions for an applicable replacement, I will need just a bit more information regarding your balances and sash.

First, can you please tell me the weight of your sash? To find out, all you must do is simply remove it from your window and place it on a scale.

Second, please refer to the following chart and identify your bottom shoe from the examples given. This will help us decide what Series channel balance you will need.
A SWISCO guide to identifying balance shoes.
A quick learner from Florida says:
The sash weighs 30 pounds. The shoe appears to be the 15-004 with wings and 1 3/32" in depth. On one sash, that works easier than the others, the local source replaced the original window balance "34-9 FA2 CMC 19" pictured, with one coded "86 34-9 JA5" since he had no more of the originals in stock. The shoes appear the same but are green in color.
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Donna from SWISCO responded:
If the balance measures 35" in length, choose 35" Series 385 channel balance with stamp option 3450

S385-35 with stamp 3450 will carry a window sash weight range of 30 through and including 34 pounds.

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
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