Air Cleaner - Thermostatic Ford LTD Crown Victoria I

DESCRIPTION

All passenger cars are equipped with a system for preheating the air entering the carburetor or the fuel injection unit during cold engine operation.

This system maintains incoming air temperature to a point where the carburetor or fuel injection system can be kept lean to reduce hydrocarbon (HC) emissions, and reduces carburetor icing.

This system consists of an air cleaner assembly with integral air control door, vacuum control temperature sensor, vacuum motor, heat shroud (on exhaust manifold), heated air tube and vacuum hoses. Some models also use additional controls such as vacuum traps and cold weather modulators.

Exploded View of Typical Thermostatic Air Cleaner Assembly Courtesy Ford Motor Co. Scheme 39

OPERATION

The air control door temperature sensor closes when the temperature of air entering the air cleaner is less than the calibrated temperature of the temperature sensor. This allows engine vacuum to operate the air control door vacuum motor, and warm manifold air to be routed to the carburetor.

When engine vacuum is applied to the vacuum motor, the air control door closes off the intake of outside air. Air is then drawn into the air cleaner from around the exhaust manifold.

As air inside the air cleaner warms, the temperature sensor begins to open, bleeding off vacuum to the vacuum motor. As vacuum to vacuum motor decreases, the air control door begins to open.

As air control door opens, outside air is allowed to enter air cleaner assembly. When air entering air cleaner reaches a predetermined temperature, the air control door opens completely, and closes off the intake of heated air.

Thermostatic Air Cleaner Assembly with Temperature Sensor & Vacuum Motor. Scheme 40

VACUUM CONTROL TEMPERATURE SENSOR

The vacuum control temperature sensor controls the operation of the air control door. During initial start-up situations, this valve directs engine vacuum to the air control vacuum motor. The motor closes the air intake door allowing the intake of heated manifold air. When the intake air temperature reaches a precalibrated value, this valve opens allowing the intake of cooler outside air.

Thermostatic Air Cleaner Assembly Showing Airflow into Carburetor. Scheme 41

COLD WEATHER MODULATOR

Carbureted Ford Motor Co. vehicles have a vacuum modulator located in the air cleaner. During engine operation in cold weather, it prevents the air control door opening to outside non-heated air for periods of at least 2 minutes even when the vacuum control temperature sensor is commanding the open signal.

1. Tape a thermometer close to vacuum control temperature sensor located inside air cleaner. Leave wing nut(s) off top of air cleaner so that top can be quickly removed to read thermometer during test.
2. With engine cold, temperature below vacuum control temperature sensor specifications, check air control door in air cleaner. It should be in fully open position (open to outside air).
3. Start engine. As soon as engine starts, door should move to fully heated air position (closed to outside air). Continue running engine and watch air control door. When door reaches fully open position, quickly remove air cleaner top and read thermometer.
4. Compare thermometer reading with specifications. If reading is not to specification, perform vacuum motor test. If vacuum motor is okay, replace sensor.

VACUUM OPERATED DUCT TEST

1. Apply parking brake and block wheels. Remove cover and element from air cleaner. Inspect the heat riser tube for damage and check to make sure it is properly installed. Remove components necessary to make sure that the duct door is open to fresh air. Check for binding.
2. Check vacuum source and condition of vacuum hoses to bi-metallic sensor, cold weather modulator and vacuum motor. Start engine. If the duct door has moved to closed to the "heat on" position, go to step 5). If the door stays in "heat off" position, (closed to warm air), block the bleed of the bimetallic sensor.
3. Duct door must move rapidly to the "heat on" position. If the door does not fully move to cold weather modulator position, replace vacuum motor and repeat test. With engine off, cool bi-metallic sensor and cold weather modulator by spraying with refrigerant for 20 seconds. Do NOT spray when engine is running or poisonous gas will be created.
4. Restart engine. Duct door should move to the "heat on" position. If door fails to move or only moves part way, replace sensor. Cool cold weather modulator and sensor.
5. Start and run engine for less than 15 seconds. Duct door should move to "heat on" position. Shut off engine and watch duct door. On all vehicles without cold weather modulator, the valve should return slowly to the "heat on" position.
6. On all vehicles with cold weather modulator, the valve should stay in the "heat on" position for at least 2 minutes. If it does not stay for 2 minutes, replace the cold weather modulator and repeat this step after cooling cold weather modulator and sensor.

AIR CONTROL DOOR CLOSING VACUUM

Using a vacuum pump with gauge, apply 16 in. Hg of vacuum to motor side of modulator. Determine if modulator holds or leaks within the correct temperature range. See COLD WEATHER MODULATOR SPECIFICATIONS.

COLD WEATHER MODULATOR SPECIFICATIONS