How to Test Electric Components with a Multimeter

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One of the most important tools in your toolbox — both physically and in terms of your own experience and know-how — is a multimeter. Most people are leery of working with electricity, and for good reason: electricity can be dangerous when working on any appliance, and knowing when you’re doing something right or wrong can be tricky. Most appliances with electrical components go bad when some part of the circuit is no longer conducting electricity correctly, so being able to isolate the parts and test them will be a frequent part of your job. Here’s how:

How to Test Appliance Parts with Your Multimeter

The first step in any repair or troubleshooting job is to disconnect the appliance from the power source. This is true whether the device plugs into the wall or is hardwired into the house; in that circumstance, you’ll need to turn off the circuit breaker. This keeps both you and the customer safe, as well as the appliance and the house.

Then, you need to dismantle the appliance based on your best guess of the problem. If a microwave isn’t powering on, it could be the magnetron, or the transformer, but capacitors and diodes are the most likely components to break. WARNING: Working on a microwave can be dangerous and even life threatening, be sure you have been properly trained before attempting.  If you’re working on an appliance that’s supposed to generate heat, isolate components from the heat circuit. Knowing which parts are more likely to break or cause any of the most common problems helps you save time and means you only need to dismantle the appliance far enough to give you access to the likely culprit.

Once you have the component out of the appliance, you’re ready to use the multi-meter. These devices test a lot of things, and the most common are continuity, voltage, and resistance:

  • Continuity tests measure if electricity can flow through the part. Plug the two probes into the multimeter and set the dial to ‘continuity.’ If you place the red and black probes on either side of the part (some parts have diodes and are one-directional so you need to arrange the probes accordingly), and you get a read of approximately zero, electricity can flow through the part. If it can’t, your multimeter will go towards one or displays OL for open loop.  The question is whether electricity is supposed to flow through or not.
  • Resistance tests how much current is lost as electricity flows through a component or circuit. It’s measured in ohms, and it is slightly more complicated to test than continuity. Whereas continuity works on a range of zero to one (or OL), resistance can come in different strengths so you need to know how much resistance a given part should have. Then you’d manually set the range on your multimeter around that amount so the multimeter can provide a readout of if the resistance is lower or higher than that amount. You can fine tune the range by making it lower if the multimeter reads close to zero or by making it higher if it read one or OL (overload). Once you have a range in the device, place the probes on either side of the device to find the ohms of resistance.  The component should be isolated from any power source otherwise you can ruin your meter.  We prefer the use of an analog meter to accomplish this. 
  • The third common test is for voltage, or the force of the electric pressure. You’ll need to know whether the appliance is DC (direct current) or AC (alternating current). Checking voltage can be very dangerous, be sure to get the proper training before attempting. Just like with resistance testing, you’ll need to manually set the expected range and make sure both the multimeter can handle the maximum expected voltage. Some components can be electrically ok, but a voltage check can ensure it is mechanically ok.

When you’re testing components, always start with continuity. Both resistance and voltage tests rely on electricity passing through the part, and the multimeter won’t know the difference between a part with the wrong resistance and a part with no continuity. You have to have the continuity information as a baseline for reading your other results.

Most people aren’t familiar with how to use a multimeter or what to do with the results once they have them. Becoming familiar with the common tests, what the readouts should be on functioning parts, and how to use the results to take next steps are some of the most important parts of the job. Go to Fred’s Appliance Academy here to learn more about how to fix parts and start learning which parts to test first on different appliances.