PGT Single Hung Balance issues

Our PGT Single Hung SH-4000 in the bathroom is having channel issues - the left hand channel will not retract with the window so I am unable to close the window completely, and therefore cannot lock it.

I have removed the channel balances, and here is what I can report: The metal channel is 18" long. The stamped number is " 17 1 NL BSI" The bottom show is about 1/18 wide".

What I cannot tell is, does the bottom shoe have some means of engaging the hook that fits into the window frame? I can't figure out why the left side channel consistently drops below the window (while the right side goes all the way to the top and doesn't seem to move with the window at all. To get the window out, I had to use a screwdriver to push the metal channel down below the take-out clip on the right side. Perhaps the springs have just had it, and I need new channels?)

Any advise is greatly appreciated!

Thanks,
Melanie

Thank you, Tom, for your reply. Here's what I eventually figured out about the channel issues (left side was not retracting with the window when it was raised, and the right side was "escaping" from the top sash guide and ending up stuck at the top of the window frame).

After removing the window I found nothing wrong with the top sash pieces nor the springs. I replaced the window, and it seems to be working just fine, AS LONG AS I PUSH DOWN ON BOTH SIDES EVENLY TO CLOSE IT. If I push down on one side only, that shifts the window in the frame, and allows that channel guide to pop out of the top sash piece. So, I think I'll be okay, as is, if I pay attention and open and close the window with 2 hands!

It may be that I'll need a new balance at some point, but for now, I think I'm good!

Melanie