What setting on a multimeter will best troubleshoot the accuracy of a type J T/C?

To troubleshoot the accuracy of a type J thermocouple (T/C), the most appropriate setting on a multimeter is millivolts. Type J thermocouples generate a voltage that varies with temperature; specifically, they produce a millivolt output that corresponds to the temperature it measures. This output is typically in the range of a few millivolts per degree Celsius.

Using the millivolt setting on a multimeter allows the technician to accurately measure the small voltage output from the thermocouple. This measurement can then be compared against known reference values or a calibration chart to determine whether the thermocouple is operating correctly and accurately reflecting the temperature it is meant to measure.

The other settings, such as resistance or voltage (AC or DC), do not provide the appropriate response required for troubleshooting a thermocouple's accuracy. Resistance measurements are generally used for checking the continuity of circuits or components, while AC or DC voltage settings deal with different types of electrical signals that do not pertain to the millivolt output characteristic of thermocouples. Therefore, the millivolt setting is the most relevant and effective choice in this scenario.