Thermo Time Switch: Testing and Inspection

Fig. 1 Thermo time switch triggering time:

Coolant temp. must be at least 5°C (9°F) below the minimum cut-off temp (stamped on the thermo-time switch).
1. Unplug the electrical connector from the cold start injector, and connect a test light across the terminals on the plug.
2. Prevent engine from starting by removing the coil wire from the distributor cap and grounding it.
3. While cranking the engine, note how many seconds the test light stays on.
4. If not within specification, Fig. 1, replace the thermo-time switch.
NOTE: Some vehicles are equipped with a pulse relay which supplies current to the cold start injector. On a cold engine, after the continuous current from the thermo-time switch shuts off, a pulsed current will continue while cranking. On a hot engine, after about two seconds of cranking, pulsed current will be supplied to the injector.