VACUUM ACTUATED
The Thermostatic Air Cleaner (TAC) system is designed to preheat air charge entering combustion chamber. Regulator door, part of the air cleaner snorkel assembly, maintains air temperature at a point where carburetor/throttle body can be calibrated much leaner to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions, while also improving warm-up driveability and reducing carburetor icing.
Vacuum actuated systems consist of air cleaner assembly, integral air regulator 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.
VACUUM ACTUATED (S & T MODELS)
When temperature of air entering air cleaner is less than setting of temperature sensor, sensor closes. This allows engine vacuum to operate directly on vacuum motor, which closes regulator door assembly to outside air. Heated air is then drawn from around exhaust manifold, through heat shroud and into air cleaner. (Scheme 182)
As air inside air cleaner warms, bimetallic sensor valve begins to open. This gradually bleeds off vacuum to vacuum motor. As vacuum to vacuum motor drops, regulator door begins to block off hot air delivery. This allows outside air to enter air cleaner. When air entering air cleaner reaches a specified temperature, regulator door opens completely, thus closing off supply of heated air from around exhaust manifold.
Scheme 182
WAX-PELLET ACTUATED (ALL OTHERS)
When temperature is less than 40°F (4°C), the wax material is in a solid (contracted) state. A calibrated spring closes integral regulator door to cold air inlet. As incoming air warms, the wax material expands by changing to a liquid state, gradually forcing out a piston against spring pressure. As piston moves, the regulator door closes down, allowing a mix of cold and heated air to enter engine. As piston becomes fully extended, heated air delivery is entirely blocked off.
Scheme 183
- With engine cold and not running, check regulator door. It should be in open snorkel position. Place thermometer inside air cleaner, near sensor.
- With engine temperature less than 80°F (27°C), start engine and run at idle. Regulator 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 (S & T MODELS)
- Check all hoses and connections for proper hook-up. With engine off, observe regulator 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. Regulator 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. Regulator door should remain closed. If not, replace diaphragm assembly.
- Remove air cleaner assembly. Cool air cleaner to less than 40°F (4°C). Integral regulator 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, regulator door should slowly open to allow cold air to enter engine.
- If air cleaner does not operate properly, ensure regulator door is not binding. Ensure calibrated spring is properly installed. If door and spring are okay, replace wax-pellet actuator.