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Line voltage for one side of the basket lift motor circuit is tapped from a “piggy-back” terminal on the line side of the transformer. Line voltage for the other side of the circuit is supplied via the basket lift relay. 24VAC is supplied to the equipment by placing the master ON/OFF switch in the ON position, which grounds the transformer. 6.4.2 How the Computer Works The SMS III computer provides the interface between the operator and the system components. The computer is powered by 24VAC supplied through Pins 1 (hot) and 2 (ground) of the 15-pin wiring harness. Internal circuitry senses the water level, water temperature, and element temperature. Depending upon the conditions sensed, the computer energizes or de-energizes the solenoid valve to control water level and the heating elements to control water temperature. The computer also controls the lowering and raising of the basket lift, and activates an audible alarm to signal the operator that a cooking cycle has completed. A rectifier in the computer coverts 24VAC to the 6-10 24VDC required by the basket lift relay and the solid-state heating relays. The computer signals for heat via Pin 4, grounds the solenoid valve via Pin 6, and senses water level via Pins 7 (low) and 9 (full). The temperature probe connects to Pins 13 and 14. The basket lift relay connects to Pins 10 and 12. The sound device connects to Pin 11. 6.4.3 How the Autofill/AutoSkim System Works The heart of the automatic filling (Autofill) system is a normally closed solenoid valve that opens when 24VAC is applied. The ground for the solenoid is supplied (via Pin 6 of the computer wiring harness) so long as the upper water-level sensor is not in contact with the water in the cookpot. When the water in the cookpot reaches the upper water-level sensor, the sensor is grounded. This causes the computer to break the solenoid ground, closing the valve. Starch or lime build-up on the upper water-level sensor may keep a ground from forming, therefore always make sure the sensor is clean and its lead (Pin 9 of the computer wiring harness) is firmly connected. Also, in order for the ground to form, there must be some mineral content in the water (pure water is non-conductive). Consequently, the units will not operate with distilled water. If distilled, highly filtered, or purified water is used, add .-cup of baking soda to the water each time the cookpot is emptied and refilled. When the AutoSkim feature is activated by pressing the skim switch on the computer, a logic circuit in the computer automatically opens the solenoid valve for three seconds every minute until the switch is again pressed. If the Autofill feature is working properly, failure of the AutoSkim feature will be due to a malfunctioning computer and not the solenoid valve. (Proper operation of the Autofill feature can be determined by draining water from the cookpot until the water level is below the upper water-level sensor. If the solenoid valve opens and then closes when the water in the cookpot again reaches the upper water-level sensor, the Autofill feature is working properly.) 6.4.4 How the Water Heating System Works To prevent energizing the heating elements when there is no water in the cookpot, these units are equipped with a low-water-level sensor. This sensor must be grounded by contact with water in the cookpot before the control circuitry will apply power to the elements. Starch or lime build-up on the low-water-level sensor may keep the ground from forming, therefore always make sure the sensor is clean and its lead (Pin 7 of the computer wiring harness) is firmly connected. In order for the ground to form, there must be some mineral content in the water (pure water is non-conductive). Consequently, the units will not operate with distilled water. If distilled, highly filtered, or purified water is used, add .-cup of baking soda to the water each time the cookpot is emptied and refilled. In addition to the low-water-level sensor discussed above, the water heating system has six more parts: the high-limit thermostat, the temperature probe, the contactor, the element, a group of three solid-state relays, and the computer. The high-limit thermostat functions as a normally closed switch. If the water in the cookpot falls below the low-water-level sensor but the sensor remains grounded (for whatever reason), the high- limit switch will open when the element temperature reaches 400.F ±15 (204.C ± 9). This cuts power to the contactor coil and thus to the element. 6-11 The temperature probe is used only when the unit is in the simmer mode. When the operator selects the simmer mode, logic circuits in the computer monitor the temperature of the water and cycle power to the element on and off as required to maintain the temperature at the setpoint programmed into the computer. The contactor is the terminal block to which the element leads are connected and where actual contact is made between the leads and the line voltage. B...

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