VACUUM ACTUATED
The TAC system is for preheating air entering carburetor. Vacuum motor, part of the air cleaner, maintains air temperature at a point where carburetor/throttle body can be calibrated much leaner to reduce hydrocarbon (HC) emissions while also improving warm-up operations and reducing carburetor icing.
Vacuum actuated systems consist of air cleaner assembly, integral air control door, vacuum control temperature sensor, vacuum motor, heat shroud (on exhaust manifold) with connecting pipe and vacuum hoses. Some models use additional controls, such as vacuum traps and cold weather modulators. Wax-pellet actuated systems consist of a self-contained wax-pellet actuated assembly, calibrated spring, integral air control door, heat shroud and connecting pipe.
Scheme 199
Scheme 200
When temperature of air entering air cleaner is less than setting of temperature sensor, sensor closes. This allows engine vacuum to operate vacuum motor, which closes damper assembly to outside air. Heated air is then drawn from around exhaust manifold, through heat shroud and into air cleaner.
As air inside air cleaner warms, sensor valve begins to open. This bleeds off vacuum to vacuum motor. As vacuum to vacuum motor drops, air control door begins to open. This allows outside air to enter air cleaner. When air entering air cleaner reaches a specified temperature, air control door opens completely, thus closing off supply of heated air from around exhaust manifold.
WAX-PELLET ACTUATED
When temperature is below 40°F (4°C), the wax material is in a solid state (contracted). A calibrated spring closes integral air door to cold air inlet. As incoming air warms, the wax material expands by changing to a liquid state which forces out a piston against spring pressure. As piston moves, the air door allows a mix of cold and heated air to enter engine.
VACUUM CONTROL TEMPERATURE SENSOR TEST
- With engine cold, check damper door. It should be in open snorkel position. Place thermometer inside air cleaner, near sensor.
- With engine temperature below 80°F (27°C), start engine and run at idle. Damper door should be in closed snorkel position. When door starts to open, read thermometer in air cleaner. Temperature should be 100-140°F (38-59°C). If door does not begin to open at this temperature, replace sensor.
VACUUM MOTOR TEST
- Check all hoses and connections for proper hook-up. With engine off, observe damper door through snorkel opening. Door should be open to outside air.
- With external vacuum unit, apply 7 in. Hg vacuum to diaphragm assembly, through hose disconnected at sensor. Damper door should close when vacuum is applied. If not, check for vacuum leak, or binding linkage.
- With vacuum applied, bend hose to trap vacuum in diaphragm assembly. Damper door should remain closed. If not, replace diaphragm assembly.
- Remove air cleaner assembly. Cool air cleaner below 40°F (4°C). Integral air door should close off cold air inlet. Ensure gasket between air cleaner and throttle body injection unit is okay.
- Install air cleaner. Ensure heat stove tube is connected between air cleaner and heat shroud. Start engine. As air cleaner warms up, integral door should slowly open to allow cold air to enter engine.
- If air cleaner does not operate properly, ensure integral door is not binding. Ensure calibrated spring is properly installed. If door and spring are okay, replace wax-pellet actuator.