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FORD BRONCO -> ENGINE & COOLING; swaps, specs, snorkels, vac. diagrams... -> Intake - Filter, Manifold, Snorkel -> Thermostatically Controlled Air Cleaner (TCAC) System
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Thermostatically Controlled Air Cleaner (TCAC) System Depiction & Overview; "...This system consists of a heat shroud which is integral with the right side exhaust manifold, a hot air hose and a special air cleaner assembly equipped with a thermal sensor and vacuum motor and air valve assembly. The temperature of the carburetor intake air is thermostatically controlled by means of a valve plate and a vacuum override built into a duct assembly attached to the air cleaner. The exhaust manifold shroud tube is attached to the shroud over the exhaust manifold for the source of heated air. The thermal sensor is attached to the air valve actuating lever, along with the vacuum motor lever, both of which control the position of the air valve to supply either heated air from the exhaust manifold or cooler air from the engine compartment. During the warm-up period, when the under-the-hood temperatures are low, the thermal sensor doesn't exert enough tension on the air valve actuating lever to close (heat off) the air valve. Thus, the carburetor receives heated air from around the exhaust manifold. As the temperature of the air entering the air cleaner approaches approximately 110°F (43°C), the thermal sensor begins to push on the air valve actuating lever and overcome the spring tension which holds the air valve in the open (heat on) position. The air valve begins to move to the closed (heat off) position, allowing only under-the-hood air to enter the air cleaner. The air valve in the air cleaner will also open, regardless of the air temperature, during heavy acceleration to obtain maximum airflow through the air cleaner. The extreme decrease in intake manifold vacuum during heavy acceleration permits the vacuum motor to override the thermostatic control. This opens the system to both heated air and air from the engine compartment..."
Source: by Chilton
Thermostatically Controlled Air Cleaner (TCAC) System; "...This system consists of the Air Control Actuator (ACA), and the thermosensor. The TCAC system controls the temperature of intake air by mixing warm, preheated air, and cold air to help improve fuel vaporization and engine warm-up characteristics. The thermosensor senses the inside temperature of the air cleaner, and opens and closes its valve. The vacuum from the carburetor is transmitted to the ACA diaphragm when the thermosensor's valve is closed and not transmitted when open. A damper is linked to the ACA diaphragm and opens or closes the warm air duct according to the movement of the ACA diaphragm. When the engine is started during cold weather, the thermosensor is closed because the temperature of the intake air in the air cleaner is low. therefore, the vacuum is transmitted to the ACA diaphragm, which then pulls up the damper to open the warm air duct fully. As the engine is warmed up, the temperature of the intake air coming into the air cleaner from the warm air duct rises and the thermosensor starts opening. As a result, vacuum to the ACA diaphragm decreases, and the damper pushed down by the spring force closes the warm air duct opening. In this state warm air and cold air are mixed together and enter the air cleaner. When the engine is operating at high rpm and under high load condition, the temperature of the air coming from the warm air duct rises very high, causing the thermosensor opening to become even larger and the damper opening smaller due to the decreased vacuum. That is, the warm air amount decreases and the cold air amount increases. When throttle valve is fully opened, the damper closes the warm air duct due to very small vacuum applied to the ACA diaphragm... " READ MORE for TESTING & R&R
Source: by autozone.com