Well I'd take a peek into the window around dusk and see how dark it looks in there. One simple thing to try would be a small battery operated light that can just be stuck in the coop. Light it up around dusk to see if that makes the space more attractive to them.
If it's been hot out, the enclosed portion is likely even warmer, which would cause them to not want to go in. Are there any openings/vents in the wall facing into the run portion? If not, I'd consider opening up that wall as much of that as possible (taking out boards and replacing with wire mesh) to increase ventilation. That will also bring in a little more natural light into that space.
If it's been hot out, the enclosed portion is likely even warmer, which would cause them to not want to go in. Are there any openings/vents in the wall facing into the run portion? If not, I'd consider opening up that wall as much of that as possible (taking out boards and replacing with wire mesh) to increase ventilation. That will also bring in a little more natural light into that space.
