Automatic Transmission

If ambient temperature is below 70°F, temperature switch (in control unit assembly) will be open and NOx system will be inoperative. When ambient temperature is above 70°F, temperature switch will be closed and circuit will continue to speed switch and vacuum switch. At speeds below 30 MPH, speed switch will be closed completing a circuit to ground. This will energize solenoid vacuum valve, shutting off vacuum to distributor advance unit. At speeds above 30 MPH, speed switch will be open, de-energizing solenoid vacuum valve which allows vacuum to reach distributor advance unit. Vacuum switch (located in control unit assembly) is controlled by intake manifold vacuum. During periods of acceleration when intake manifold vacuum is low, vacuum switch energizes solenoid vacuum valve which shuts off vacuum to distributor advance unit. Therefore, when temperature is above 70°F at speeds below 30 MPH or during periods of acceleration there will be no vacuum to distributor advance unit.