Repair or Replace Window

[Michael Craig]

Hello,

I have one window in an apartment that will not stay up. I believe it is less than 10 years old. It is made of Plexiglas with nice trim around it so I really do not want to replace it. However, there are no balance mechanism to hold it up - the sash slides freely in the frame. Is there anything I can install in the frame that will prevent the window from falling? Note, I cannot remove the sash as the frame encompasses the sash and there are no sash retainers.