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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
⅛-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 ⅛-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 400ºF ±15 (204ºC ± 9). This cuts
power to the contactor coil and thus to the element.