marvin windows slam shut

A handy person from wilbraham, ma says:
May 9, 2020
The window won't stay open, it slams shut. They are marvin double hung windows. the number stamped on the channel is 22HD P on the left side its stamped 22 U The window are about 25 years old.
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Tom from SWISCO responded:
May 13, 2020

It definitely sounds like you need new balances. I recommend our S751-23 channel balance. This should work well for you, though I'm not sure which of our stamp options would be the equivalent of "22U." That's not one I've ever run into. You should weigh your sash and refer to the chart on our S751-23 store page to confirm the best choice.
23" Series 751 Channel Balance
23" Series 751 Channel Balance
S751-23
$10.98
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