The thermostat is mounted in the air filter head and ensures the switching of the intake air line (photo).
To check, remove the air duct and start the engine. Observe the thermostat with a mirror. On a cold engine, the thermostatic divider damper must close the cold air duct (photo). As the engine warms up (after 10-15 minutes) damper should open. The degree of opening is determined by the ambient temperature.