All of us techs are carrying around multimeters these days, and that means we have several different voltage measurement settings available to us at any given time. Usually these are DC voltage, AC voltage, and LoZ (low input impedance). Each of these functions has a specific use, and part of taking a voltage measurement is picking the correct setting for the job.

LoZ is by far the most common voltage function you should be using. In fact, there is almost never a time when you should do an AC voltage measurement with the standard VAC function of your meter. LoZ is a much more reliable measurement, for reasons I covered in this post.

But when it comes to measuring DC voltage across a load in the appliance, you need to always use the DC function on your meter. That may sound obvious, but it means that you have to have a functional understanding of the component that you're measuring and know what its power supply is by reading the schematic. Thermistors, for example, are always low voltage DC components, and therefore need to be measured with the DC function of your meter.

In fact, there's an interesting thing that happens if you try to use the LoZ function on a low-voltage DC circuit, like a thermistor circuit. Because of the relatively low impedance of the meter on this setting (about 3 kohms, as opposed to the 50 megaohms that the normal AC and DC functions have), current will flow through your meter -- way more current than the puny DC power supply is equipped to handle. This will result in loading down, causing your meter to read 0 volts even in a circuit with a good voltage supply, all because you're using the wrong setting for measuring a thermistor.

If you want to troubleshoot thermistors like a champ, you should check out these exclusive, premium-member-only webinar recordings right here at Appliantology.