Many modern replacement windows are vinyl and run on a spring system. The springs are located on the sides of the window in the frame. They control the tension when opening and closing the window. If the spring becomes too loose and worn, the window may begin to slowly close on its own after having been opened. On the other hand, a new spring may be too tight and cause the window to stick. In either case, the spring needs to be adjusted.
Open the bottom half of the window approximately 3 to 4 inches wide.
Tilt the top half of the window inward. Do this by opening the top half 1 to 2 inches. Then press the tabs on the sides of the window downward. The window sash will release from the frame and you will be able to tilt it towards you.
Push upward on one corner of the upper sash that is now tilted in. Do this until the window pops out of its attachment in the frame, also known as the shoe.
Twist the upper sash to release it from the remaining shoe. You will feel it pop when it releases. You will now be able to pull the upper sash from the window frame.
Find the spiral balance, or spring, with a T-shaped hook on it. This is located inside the frame and attached to the shoes where you just released the window.
Grab an end of the spiral balance using needle-nose pliers. Pull downward and away from the shoe.
Tighten the spiral balance by turning it clockwise. Loosen it by turning it counterclockwise. Typically, one turn will balance the window. Perform the same task on the other side of the window.
Insert the bottom of the top sash back into the window frame. Click the two bottom corners in their respective shoes. Push the top of the window into the top portion of the frame until it clicks into place.
Test the window by opening the bottom and top sashes. Also, leave them unlocked for several hours. If the sashes move up and down smoothly, the tension is not too tight. If they don't fall while unlocked, the tension is not too loose.