Thermo Time Switch: Description and Operation

The cold start thermoswitch, located on the left side of the engine block near the knock sensor, is used to control the operation of the cold start valve. The switch operates as a circuit breaker for the cold start valve. When the engine temperature is below a specified value, the thermoswitch will complete the cold start valve electrical circuit to ground. The injector will be energized as long as the circuit is completed.

A temperature sensitive bi-metallic contact and a heating element are incorporated into the switch. The heating element, like the cold start valve, gets power when the ignition is in the start position. When the engine is cranking, the heating element is warming up. If the engine is cranked for more than a few seconds, the bi-metallic contact will distort from the heat of the heating element, opening the switch and turning the cold start injector "OFF". This is to prevent "flooding" in the event the engine does not start right away.

If the engine temperature is greater than the specified value, the valve will be warm, the bi-metallic contact will be distorted, and the switch will be open so the cold start injector does not operate.