Air filter with thermostat (Honda Accord 3)

This is a temperature controlled device that improves hot engine performance and reduces carburetor icing. The air cleaner assembly is equipped with a vacuum controlled air flow control diaphragm at the inlet and a bimetallic air inlet valve inside the air cleaner. The air inlet valve is closed when the temperature of the air being cleaned is less than 25°C, thereby allowing manifold vacuum to open the air control diaphragm and supply heated air to the carburetor. If a vacuum is detected at the inlet of the air control diaphragm at a higher temperature and air leaks, the valve is defective and must be replaced. When checking this system, make sure that the hot air pipe is connected to the base of the intake duct and the other end is connected to the exhaust pipe. Fresh air is heated, blowing over the exhaust pipe and through the hose enters the carburetor.

Very often the hose is disconnected when removing the air filter and then skipped during installation. This causes problems when operating the car in cold conditions.