To troubleshoot thermocouple readings, you should determine if the error is from the cold junction sensor, A/D conversion, or the signal itself. If the cold junction reading is off, it will affect the calculated thermocouple temperature. To isolate the issue, you can remove the thermocouple and jumper the analog input to GND, which should give a 0.0V reading. Another option is to remove the thermocouple and measure the air temperature near the LabJack. The expected voltage will depend on whether the terminals being connected to are at air temperature or warmer.