When the radio is first shown in Norma's apartment, the brand name is covered with tape. But as the camera pans past the radio at about the 12:00 point, the tape is gone and the word "ZENITH" is visible where the tape was before.
When Norma wakes up in the coldness reality at least one of her sun pictures is lying up again the wall. It shouldn't be in her apartment since it was painted in her mind during the hot dream.
When Mrs. Bronson faints, she falls backward. A person that faints falls forward.
When the Intruder opens Norma's fridge door to get water, the light is on in the fridge despite the power being off.
After Norma's line "current's off again", it can be faintly heard again right after that. That is Norma's own voice again. This was caused when the magnetic tape spun around and came in contact with itself again on the reel. The magnetized tape then transferred the magnetic imprint to a silent part of the tape. This is sometimes called "print through."
The Earth moving closer to the sun would raise the temperature, but it wouldn't create a "midnight sun". That would require a change in rotation - either stopping it or drastically changing the axis.
The plot of this story is that the temperature is unbearably hot. However, the man who breaks into the apartment is wearing a sports coat.