Window keep going down not holding up

Hello, thank you for posting, 

Your window appears to use the 15-191 pivot shoe that is compatible with either the 1/2" thick Series 160 coil springs or the 3/8" thick Series 165. You will need to remove the assembly to measure to confirm the correct fit. 

Alternate image for 15-191

If you need assistance with choosing the correct weighted coils, please provide the thickness of the original coil spring and the weight of the window sash to move forward. The window sash will need to be removed and placed on a scale. 

Let me know if you have any additional questions!