[Motor31]

Look for a gap in the area where the sliding windows mate together. Mine tend to leak air in the upper seam between the fixed upper and lower windows.

Keep in mind that the R value of even the dual pane windows is pretty small. That quarter inch gap doesn't stop much temperature transfer.

If you are getting air flow around the frame area then you will need to pull the window and put window putty where the outside frame mates to the side of the wall. On mine one of the slide windows had putty installed but the fine amish craftsman put it on the inside edge of the frame where it did not mate to anything. As a result when it rained I had a water wall on the inside of the slide out next to the recliner.