When the temperature of the incoming air rises due to its heating by the exhaust manifold, the wax capsule in the vacuum switch closes the switch, blocking the vacuum to the inlet air temperature control valve. Since the vacuum is closed, the air intake flap moves and closes the control valve at a temperature of about 40°C. In this case, only cold air from the front of the car enters the engine.
Examination
Cool the engine, then separate the intake port from the front of the air cleaner housing. The flap valve of the control valve must shut off the hot air supply. Start the engine. The flap must then immediately rise and block the cold air supply and, after the engine has warmed up, must move and open the cold air supply only.
To test the vacuum switch, disconnect the vacuum pipe from the control valve and plug the pipe with your finger. When the engine is cold, vacuum should be felt in the tube, and after the engine warms up to normal operating temperature, there should be no vacuum.
To check the operation of the intake air temperature control valve, separate the intake duct from the air filter housing. The flap valve should shut off hot air to the engine. Disconnect the vacuum pipe and create a vacuum in it. In this case, the flap should move and block the flow of cold air into the engine.
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