Thermactor Air By-Pass (Control) Solenoid
This solenoid reacts the same as the pressure-type EGR solenoid; that is, it is normally closed, blocking air pressure flow until energized. The upper port is connected to the Thermactor by-pass valve top actuator port. The lower port is connected to manifold vacuum. See Fig 2.
When the ECA energizes the solenoid, manifold vacuum is applied to the by-pass valve, allowing air pump air to be injected into the exhaust ports. When de-energized, the by-pass valve "dumps" air pump pressure to the atmosphere. The ECA uses information from the air inlet sensor and throttle position sensor to determine when to inject or dump air pump air.