| A mechanical or electricallydriven propeller that draws or pushes air through the radiator, condenser, heater core or evaporator core. | |
| Air injection reaction system | |
| Evaporative emission system. | |
| A signal that varies the ratio of on-time to off-time, resulting in a square wave that can range between zero and 100; in a process, the ratio of on-time to total cycle time; in fuel injectors, the percentage on-time to total cycle time; in solenoids, the percentage of on-time to total cycle time. |