The system is controlled by a wax thermostat installed in the inlet duct of the air filter housing. The thermostat moves the flap that regulates the mixing of hot and cold air. When the ambient air temperature is below a certain value, the damper is positioned so that only warm air from the housing on the exhaust manifold enters the filter, however, as the ambient air warms up, the damper moves, letting in air from outside and closing the warm air flow.
If the system is not functioning properly, the air filter housing must be replaced; since the damper cannot be replaced separately.