When you say he doesn't move, do you mean he really doesn't move? Not even when you take him out and handle him? If you take him out and put him on a table and read a book for 10 minutes, does he really not move AT ALL? Because that's potentially a sick snake.

A healthy snake, even one that's in shed, will take care of their own thermoregulation. All you have to do is provide the warm spot. Don't heat the cool side unless your house temps are really well below 70F. 75F is more than fine. If he wants a temperature in between, he can find it himself. You can provide a tube or a log (packing tubes from the UPS store work well, but you have to cut them) as an 'intermediate temperature hide' in the middle. He'll find the temperature he wants on his own, and if he wants the 75F cool side, that's what his body is telling him.

But if he's really not moving at all, even when you handle him, I'd take him to the vet.