Specifically:
* When the heater is turned ON: The thermo valve opens, allowing coolant heated by the engine to flow through the heater core. This warms the air blown into the cabin by the blower motor.
* When the heater is turned OFF: The thermo valve closes, preventing coolant from flowing through the heater core. This keeps the coolant circulating primarily through the engine's cooling system for optimal engine temperature regulation.
In short, it's a crucial component for regulating the temperature inside the vehicle. A malfunctioning thermo valve can lead to either no heat or excessively hot air from the vents, depending on whether it's stuck open or closed.
