Window coil will not keep window open

A home owner from California says:
October 29, 2020
Hi,
Looking to replace some hardware inside my window. I'm not sure what this part is called. I also don't know the manufacture of the windows. Some windows work great, you open them and they stay open, easy up and down while several others need something to keep the open and seem heavy.I would like to order a set and see if that is the issue. Please advise what ever you can. I've included a picture.
Thumbnail of the uploaded file named window coil.jpg
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Casey from SWISCO responded:
November 2, 2020

Hello, thanks for posting! Your pivot shoe is actually an older version of our 15-180. This uses our Series 190 Coil Springs. You will need to look for a stamp or imprint on your coil springs to determine which weight option to select. Good luck with your repair, and let me know if you have any further questions! 
A home owner from California says:
November 2, 2020
I've replaced the glass and the window now weighs 23.9 lbs. The window has 2 coils on each side that are labeled 540 on the coil. So I need to order 4 series 190 coil 640 to cover the new weight of the window. Please advise. Also, do these coils wear out?
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Casey from SWISCO responded:
November 2, 2020

Ah, that likely explains why some of the windows will not remain open. In that case I would agree with you on the 640. Coil springs can wear out over time. In order to minimize wear, we recommend replacing all of the springs at the same time, as pairing a new and old coil spring can cause the newer one to wear out more quickly. 
Coil Balance Shoe
Coil Balance Shoe
15-180
$3.97
Double Support Detent Clip
Double Support Detent Clip
15-181
$6.17
Balance Bushing
Balance Bushing
15-182
$1.80
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