Thermal Vacuum Valve: Description and Operation

Fig. 48 Thermovalve:

The thermovalve is mounted on the intake manifold, extending into the engine coolant passage. This valve opens and closes vacuum ports in response to engine coolant temperature. The presents or absence of vacuum at these ports serves to initiate actions in the purge control system, the EGR system and of most concern to the fuel system, the two stage choke breaker. When the coolant temperature reaches 65F~ (18~C) the thermovalve closes the port that has been preventing vacuum from reaching the second stage of the choke breaker. for description of operation for the other systems that are affected, refer to EMISSION CONTROLS.