The heat in your car is pulled out of the engine. The heater core to be exact. Your antifreeze has to be up to temp for your heater to work. Your antifreeze is heated by the engine. When you use the heater you are pulling heat out of the antifreeze thus cooling it off. Once it gets too cool the ICE starts up to heat the antifreeze back up.
For more information http://auto.howstuffworks.com/cooling-system10.htm

If you ever have a car overheating ALWAYS turn the heat and fan on full blast. It will cool the antifreeze which inturn will cool the engine.

Personally I am shocked the the TCH does not have an electric heater. At some of the long lights here in town my engine has come on and off a few times with the heat set about 79 - 81.