Channel Balance
Thanks for posting. It appears you have a Series 795 Channel Balance. We can replace this, but you'll need more information to narrow down exactly what you need. This blog article here goes into depth about how to find the exact Series 795 you need. Take a look and let me know if you have any questions.
I can not remove the window to measure it as I will likely not be able to reinstall it. I have the replacement window but need a new channel balance. Thank you.
With a stamp of 26 5, I believe you have an older model of the Series 795. The metal channel in your case should be 27" long, but you need to measure it to verify. Assuming this is accurate, then you want our S795-27.
As for the stamp, the modern equivalent of the old 26 5 would be the 27E. Two balances with this stamp can carry 26 through 30 pounds. You need to weigh your sash to verify that it falls in that range. If it's lighter, or heavier, then the 27E stamp won't work for you.
As for the balance being jammed, there isn't much you can do about that. Your first step should make sure that the pivot shoe isn't accidentally in the "locked" position, which you can change by turning the metal cam. Otherwise you could try to lubricate the window track to loosen it up some.