Air Injection Vacuum Control Solenoid Valve: Description and Operation

Dual Thermactor Air Control Solenoid Valve:

The Thermactor Air Bypass (TAB) and Thermactor Air Diverter (TAD) solenoids control whether or not vacuum is applied to the TAB and TAD valves. The EEC-IV System Module controls bypass and diverter valve operation by providing circuit ground for the Thermactor Air Bypass (TAB) Solenoid and the Thermactor Air Diverter (TAD) Solenoid.

When the engine is started and its coolant temperature is below 50~F (10~C), the ECA will not ground the TAB solenoid. The TAB Valve diaphragm remains closed by spring pressure, causing pump air to be bypassed to the atmosphere.
When coolant temperature reaches 50~F (10~C), the ECA grounds the TAB circuit and the TAB solenoid is energized. Vacuum is applied to the TAB valve diaphragm, the bypass valve opens and pump air is sent to the diverter valve. The ECA, at the same time, provides a ground for the TAD solenoid circuit, which allows vacuum to be applied to the diverter valve diaphragm. This causes the diverter valve to direct pump air to the exhaust manifold.
Once the engine is in Closed Loop Mode, 190~F (88~C), the ECA removes circuit ground for the TAD solenoid. The diaphragm is closed by spring pressure, and pump air is redirected downstream to the catalytic converter. The ECA will return the MTA System to its Bypass Mode to protect the catalytic converter from damage and overheating, when certain operating conditions are detected.