Three causes: 1) Reversed thermocouple wires. 2) A false temperature reading (like -328 degrees) resulting from a defect in the temperature measurement circuit or memory corruption. 3) Operating the kiln in a very cold environment where the thermocouple is very cold (32F or below) and the controller board temperature is much warmer (70F or above). Orton recently enhanced the software to eliminate TCR from this condition.
Other possibilities are a defect in the temperature measurement circuit, or memory corruption of the circuit board. A memory corruption error on the Orton controller is sometimes accompanied by a -328F temperature reading.
The way the kiln wires are positioned in the switch box can cause controller memory corruption:
1) Relay-to-element lead wires are wrapped around or running parallel to the thermocouple wires.
2) Relay-to-element lead wires are placed close to the back of the controller circuit board.
Keep other wires away from the thermocouple wires. The voltage reading from the thermocouple is so very small that the electromagnetic field from nearby wires can interfere with the thermocouple readings.
Make sure the thermocouple wires are connected properly at the back of the controller and at the thermocouple. Follow the color coding, which is marked at the connections. If need be, rearrange the wires in the switch box, turn the power off, and then reboot the controller.