Cold Temp. Activated Vacuum System: Operation

Temperature switch activates solenoid which is open at temperatures of 49°F (9°C) and below, and is closed at temperatures of 65°F (18°C) and above. In between these temperatures, it may be either open or closed. Below 49°F (9°C), system is inoperative and distributor diaphragm receives carburetor spark port vacuum, while EGR valve receives carburetor EGR port vacuum.

When temperature switch closes, current from battery energizes the three-way solenoid vacuum valve and carburetor EGR port vacuum is delivered to distributor advance diaphragm, as well as EGR valve. The latching relay (normally off) is also energized by closing of temperature switch. However, once on, it receives its energy through ignition switch and stays on until ignition switch is turned off, regardless of whether temperature switch is opened or closed.