New Channel balances make window too hard to close

A home owner from Largo, Fl says:
May 23, 2017
I just installed some new channel balances(order 891371) on some non tilt windows. Some windows go up & down fine but others go down hard. I have to apply a lot of pressure when they get half way down.What did I do wrong.?the #'s stamped on the original balances are, 2906,2904,2305,1730. The 1730 & 2305's seem to be working fine. thank you
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Tom from SWISCO responded:
May 25, 2017
It sounds like the options you chose may not have been appropriate for the weight of the sash. The stamps you listed are actually quite peculiar. I would recommend weighing the sash each balance supports and then referring to the chart on each balance's store page. That will tell you exactly what option you need in each case.
18" Series 380 Channel Balance
18" Series 380 Channel Balance
S380-18
$9.34
24" Series 380 Channel Balance
24" Series 380 Channel Balance
S380-24
$10.55
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