THERMO Valve
Thermo valve senses engine coolant temperature, and allows or denies vacuum to EGR valve, depending on engine temperature. Below 131°F (55°C), thermo valve is closed and no vacuum from intake manifold reaches EGR valve. Above this temperature, valve is open and EGR function occurs.
NOTE:
On 1979 California vehicles with 2.0L engine, two thermo valves are used, one of which is connected to the air control valve and not the EGR.