DS is the same way. Our air is always in between 68-72 degrees with fans all on full blast and he still sweats. So I changed him from wearing sleepers at night to just a basic onesie with socks and even then I sometimes have to take the socks off. He's also slept in his CD numerous times. Now that its colder outside I put him back into the sleepers but leave him uncovered and if hes in a onesie with socks ill put a warm blanket on him. All you can do is try and keep them cool and if everything around him is cool and he still sweats then hes simply hot natured.
DS also sweats like a pig in his carseat.