Thermostatically Controlled Air Cleaner (All Engines)

Carburetor air intake system consists of a heat stove, a corrugated paper heated air pipe and an air cleaner incorporating temperature controlled doors operated by vacuum through temperature sensor. Operation is as follows:

1. Heat stove is a sheet metal cover, shaped and bolted onto exhaust manifold. Air drawn in along lower edge of stove passes across manifold surface, picking up heat. Heated air passes through corrugated paper air pipe and enters snorkel of air cleaner.
2. Temperature controlled air cleaner is designed to mix this heated air with cold air from engine compartment so that carburetor air temperature averages 115°F. Air mixing is done by two doors which move together so that when cold air door is closed, hot air door is open and vice versa. Usually both doors will be partially open.
3. When engine compartment temperature reaches approximately 135°F, cold air door will be fully open and hot air door will be fully closed. Temperature doors are controlled by a diaphragm type vacuum motor. When there is no vacuum present in the motor, diaphragm spring forces cold air door open and hot air door closed.
   Fig 1: Carburetor System 1.1 Liter Engine Standard Transmission

   Courtesy of NOT AVAILABLE
   Fig 2: Thermostatically Controlled Air Cleaner (1.1 Liter Engine)

   Courtesy of NOT AVAILABLE
4. When engine is running, amount of vacuum present in vacuum motor depends on temperature sensor in air cleaner which is located in vacuum line between intake manifold and vacuum motor.
5. Inside sensor, a bi-metal temperature sensing spring starts to open a valve to bleed more air into vacuum line whenever temperature in air cleaner rises above 115°F. Whenever temperature falls below 115°F, sensing spring starts to close air bleed into vacuum line, allowing more manifold vacuum to reach vacuum motor. Whenever there is 9" or more of vacuum in vacuum motor, diaphragm spring is compressed, cold air door is closed and hot air door is open.
6. When starting a cold engine (air temperature under 85°F), cold air door will close and hot air door will open immediately. This is because air bleed valve in sensor is closed so that full manifold vacuum is applied in vacuum motor. Cold air door will remain closed only a few minutes. As air cleaner receives hot air from heat stove, sensor will cause cold air door to open partially, mixing cold air with hot air as necessary to regulate air cleaner temperature within 20°F of the ideal 115°F.
7. While air cleaner temperature is being regulated, accelerating engine hard will cause vacuum level in intake manifold and vacuum motor to drop. Whenever vacuum drops below 5", diaphragm spring will fully open cold air door in order to get maximum air flow required for maximum acceleration.