For a temperature control system, you’ll need at least three things, a selector to which the temperature is set, a way to measure whether this target is reached and a regulator which makes changes to the airflow coming in.

Temperature regulation
In most aircraft the temperature in the cabin is regulated by mixing hot air with cooled air. There are two methods which are used, the mechanical and electro-mechanical. The basic not automatic method is done by valves which are manually operated to regulate the amount of hot and cold air entering the cabin. The automatic way of control for the cockpit, cabin and cargo holds is done by comparing the temperature set in the cockpit with the temperature in the cabin and the supply ducts. If there is a difference the hot air valve will be adjusted to allow more or less hot air to go through the duct until the desired temperature is reached.