There was period from the late 1800’s through the nineteen aughts and teens when it appears to have been common to locate the weight pocket access door toward the back of the jamb – the track in which the upper sash rides, closest to the outside of the house.
The practice appears to have been abandoned by the 1920’s in favor of locating the door closer to the front of the jamb.
This situation creates a couple of problems. First, it is impossible to open the access door without removing the parting strip. Second, windows from this era often have heavy coats of rock-hard paint making removal of said parting strip more difficult. And third, windows from this era were often larger, requiring longer weights that are in the way when only needing access to the lower sash weights.
Most of the time, when a sash cord needs repair, it is a cord belonging to the lower sash. So when you finally get the door open, what do you see? The weights belonging to the upper sash. And they are big honking weights. Sometimes they won’t even fit through the pocket door! (What were they thinking?) Well, you need to get this weight out of the way to try to do your repair work in the forward portion of the weight chamber. The only way to raise the weight is to lower the upper sash, but these sashes are often painted shut, eliminating access to the pulleys. What should you do with it? And how? A simple solution is to lift the weight higher into the chamber so you can fish around for the other weight. But this is often easier said than done. Trying to grab onto this this slippery beast can be a challenge. The weight chambers are often tiny, and the weights large, leaving no room to grab the weight. You can use really sticky tape or a powerful magnet to lift the weight. Then put a clamp at the top of the door opening to keep the weight from falling down. Hopefully, the clamp won’t block the opening from removing the weight belonging to the lower sash.
Locating the pocket door towards the front of the jamb just makes more sense. You simply remove the inner stop and you can pry the door open – often without removing the parting strip. Open the door, and there is your weight, ready to remove. Fish your line around the pulley, lower it, and you can see it!
There must have been some wisdom in locating the access door towards the back of the jamb, but not too much, as this practice didn’t last long.
Note: One positive reason for locating the access door to the rear of the jamb is when installing spring bronze for the lower sash, you aren’t nailing into the access door.