Coolant Temperature Override Switch
Switch is threaded into thermostat housing and incorporates a thermal unit which reacts to coolant temperatures to route either intake manifold or carburetor ported vacuum to the distributor vacuum advance diaphragm. When coolant temperature is below 160°F, ports "I" and "D" are open and port "2" is closed. This allows intake manifold vacuum to be applied through a hose connection to the distributor advance diaphragm, resulting in full vacuum advance. When coolant temperature reaches 160°F port "I" closes and ports "2" and "D" are open. Intake manifold vacuum is then blocked off and carburetor ported vacuum is applied through the solenoid vacuum valve to distributor advance diaphragm, resulting in decreased vacuum advance. Coolant temperature override switch is used on some cars not equipped with a TCS system. In this case, port "2" is connected directly to carburetor ported vacuum connection.