The heated air intake portion of the air cleaner consists of a bimetal switch and vacuum motor and a spring-loaded temperature control door in the snorkel of the air cleaner. The temperature control door is located between the end of the air cleaner snorkel, which draws in air from the engine compartment, and the duct that carries heated air up from the exhaust manifold. When the temperature under the hood is below 90°F, the control door prevents underhood air from entering the air cleaner, allowing only heated air from the exhaust manifold to be drawn into the air cleaner. When underhood temperatures rise above 130°F, the control door blocks off heated air from the exhaust manifold and allows only cooler air to be drawn into the air cleaner.
By controlling the temperature of the engine intake air this way, exhaust emissions are lowered and fuel economy is improved. In addition, throttle plate icing is reduced and cold weather driveability is improved.
- Remove the air cleaner from the carburetor and allow it to cool to 90°F. Connect a vacuum source with a vacuum gauge to the sensor.
- Apply 20 in. Hg to the sensor. The door should be in the "heat on" (up) position. If it remains in the "off" position, test the vacuum motor.
- Connect the motor to a vacuum source. In addition to the vacuum gauge, a hose clamp and a bleed valve are necessary. Connect them in the following order:
- Vacuum source;
- Hose clamp (or shut-off valve);
- Bleed valve;
- Vacuum gauge;
- Vacuum motor.
- Apply 20 in. Hg vacuum to the motor. Use the hose clamp to block the line, so that the motor will retain the vacuum. The door operating motor should retain this amount of vacuum for five minutes. Release the hose clamp.
If the vacuum cannot be built up to the specified amount, the diaphragm has a leak and the valve will require replacement.
- While slowly releasing the vacuum, check the operation of the door. The door should open at no less than 5 in. Hg.