My son just rented a small apt... it is an old house sectioned off in 3 apts... full walls in between... he has no heater or cooler... he was told the person in the middle apt. controls the heat... is this legal in the state of calif.

I assume you mean he has not thermostat but he does have hot air ducts, right? CA law does not even require that there be AC let alone your own stat. The temp must be liveable but nothing in the law says he has to be given control of it. What temps does he run into?