Green79Scottsdale
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What is this?
- Thread starter Green79Scottsdale
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chengny
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You got it. That is the temperature sensor/control valve for the Thermac system. The technical term for it is the "air bleed valve".
The Thermac system explained:
The TAC system, Fig. 82, is designed to improve carburetor operation and engine warm-up conditions. It achieves this by keeping the air entering the carburetor at a temperature of at least 100°F, or more.
Carburetor air temperature is controlled by a pair of doors, Figs. 83 thru 85, located in the air cleaner snorkel, which channel either preheated or under hood air to the carburetor.
Preheated air is obtained by passing under hood air through ducts surrounding the exhaust manifold, causing it to pick up heat from the manifold surface. The heated air is then drawn up through a pipe to the air cleaner snorkel.
Underhood air is picked up at the air cleaner snorkel in the conventional manner.
The two air mixing doors work together so that as one opens, the other closes and vice versa. When underhood temperature is below approximately 86°F., the cold air door closes, causing the hot air door to open. Hot air from the exhaust manifold stove is then drawn into the carburetor. As the underhood temperature increases, the cold air door begins to open until the temperature reaches approximately 115°to 130°F, at which time the cold air door is fully open and the hot air door is fully closed.
The doors are controlled by a vacuum motor mounted on the air cleaner snorkel. This motor, in turn, is controlled by a sensor inside the air cleaner (the air bleed valve) which regulates the amount of vacuum present in the vacuum motor according to air cleaner temperature. Whenever manifold vacuum drops below 5---8 inches, depending on the unit, the diaphragm spring in the motor will open the cold air door wide in order to provide maximum air flow.
The vacuum motor and control door assembly in the left snorkel on outside air induction units does not have a sensor and is controlled only by manifold vacuum. This snorkel remains closed until full throttle is obtained. With manifold vacuum at 6-8 inches, the door will open, allowing maximum air flow.
The Thermac system explained:
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The TAC system, Fig. 82, is designed to improve carburetor operation and engine warm-up conditions. It achieves this by keeping the air entering the carburetor at a temperature of at least 100°F, or more.
Carburetor air temperature is controlled by a pair of doors, Figs. 83 thru 85, located in the air cleaner snorkel, which channel either preheated or under hood air to the carburetor.
Preheated air is obtained by passing under hood air through ducts surrounding the exhaust manifold, causing it to pick up heat from the manifold surface. The heated air is then drawn up through a pipe to the air cleaner snorkel.
Underhood air is picked up at the air cleaner snorkel in the conventional manner.
The two air mixing doors work together so that as one opens, the other closes and vice versa. When underhood temperature is below approximately 86°F., the cold air door closes, causing the hot air door to open. Hot air from the exhaust manifold stove is then drawn into the carburetor. As the underhood temperature increases, the cold air door begins to open until the temperature reaches approximately 115°to 130°F, at which time the cold air door is fully open and the hot air door is fully closed.
The doors are controlled by a vacuum motor mounted on the air cleaner snorkel. This motor, in turn, is controlled by a sensor inside the air cleaner (the air bleed valve) which regulates the amount of vacuum present in the vacuum motor according to air cleaner temperature. Whenever manifold vacuum drops below 5---8 inches, depending on the unit, the diaphragm spring in the motor will open the cold air door wide in order to provide maximum air flow.
The vacuum motor and control door assembly in the left snorkel on outside air induction units does not have a sensor and is controlled only by manifold vacuum. This snorkel remains closed until full throttle is obtained. With manifold vacuum at 6-8 inches, the door will open, allowing maximum air flow.
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