Andersen balance 11600-2 won't hold up sash

A quick learner from East Lansing says:
June 12, 2017
A few weeks ago, I did a search on the web for sash balance 11600-2 and the web directed me to your site SWISCO and pointed out the replacement is 24-737. I ordered two of them, order # 900103, and replaced them this weekend. However, the balancers does not have enough tension on the cords, because the windows will not stay up. What can I do to fix the situation? There are other numbers on the balancer opposite of the 11600-2 and they are P29 12-31 10 81. Any help would be greatly appreciated. I have attached an image of the original sash balancer for more information.

Thank for your time.
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Tom from SWISCO responded:
June 12, 2017
I am afraid your photos did not come thru. Could you resend them again so that we may take a closer look for you?
A home owner from Lansing Michigan says:
June 12, 2017
Attached is photo you requested, hope it comes through.

Thanks,
andersen balance
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Tom from SWISCO responded:
June 16, 2017
Based on this picture, I see the stamp "12-31." I believe this is what you need. With that in mind, I recommend our 24-1231.
A quick learner from MI says:
June 16, 2017
Thank you for your help. I will order them soon. What would I do with the ones that I have, since they did not work.
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Tom from SWISCO responded:
June 19, 2017
You can return them for a refund any time you wish, assuming they haven't been modified or damaged in any way. You can see our return policy here.
Andersen Sash Balance, 1226, 1227, 1231
Andersen Sash Balance, 1226, 1227, 1231
24-1231
$54.20
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