If you’re a regular reader of this blog, you will have undoubtedly noticed that there is one tool we recommend using at the start of nearly every appliance repair: a multimeter. This device can assist you in identifying where the problem originates, whether it’s an incoming power issue or a faulty component. Is your electric oven not heating up because of a burned-out bake element? Is a defective inlet valve preventing the dishwasher from filling with water? Has the dryer’s thermal fuse blown? A multimeter can help determine this, so you can be confident you’re replacing the part that is actually causing the problem.
And it’s not just home appliance malfunctions you can troubleshoot with a multimeter. Heating and cooling product parts such as furnace igniters or central air condensing unit capacitors, as well as components on outdoor power equipment like start switches or batteries, can be tested with a multimeter as well. Simply put, a multimeter will save you time and money on your repair by taking the guesswork out of troubleshooting. Here’s an overview of what this device does and how it does it…
Multimeter basics
While multimeters comes in all shapes and sizes, they often share the same functions: the ability to measure electrical continuity, voltage, and resistance. A dial is used to select both the function and range for the test being conducted. On digital meters, an LCD display will show the reading of the function selected. The position of a needle will do the same for analog meters.
Meters will have two leads, or probes, that are used to make contact with electric terminals. The red meter lead is usually identified as the positive lead while the black lead is negative. Meters will have two or more ports available to plug the leads into. The black lead should be plugged into the common port. The red lead can be plugged into the port that will measure volts, Ohms of resistance, and current below 200 milliamps, or on some models, a port that will allow measurement of milliamps above 200, or even microamps.
How to use a multimeter to test for continuity
The most common use for a multimeter is to test for electrical continuity – a continuous electrical path present in a component. If the component fails the continuity test, it is likely defective and will require replacement. Thermostats, fuses, switches, heating elements, sensors, and solenoid coils can all be tested for continuity.
When using an analog meter for this test, first rotate the range selection dial to the lowest setting for Ohms of resistance, then calibrate the meter by pinching the metal ends of the leads together while adjusting the meter’s needle to “zero”. Calibration won’t be necessary when using a digital meter; just rotate the range selection dial to the lowest setting for Ohms of resistance, or “resistance with tone” if your meter has this option. You’re now ready to begin testing:
- Touch the black lead to one of the component’s terminals or wires and the red lead to the other terminal or wire.
- When testing a switch, fuse, thermostat, or sensor, the meter reading should indicate “zero” Ohms of resistance if the component has continuity.
- If the analog meter’s needle doesn’t move, or the digital display does not change significantly, then the component has no continuity and is likely defective.
When testing a two-terminal switch for continuity, be aware that the component will either have continuity before the switch is actuated or after. If the switch is supposed to have continuity after being actuated, it is considered to be “normally open”; if the switch is supposed to have continuity before being actuated, it is considered to be “normally closed”. Three terminal switches will have a common terminal in addition to a “normally closed” terminal and a “normally open” terminal. The common terminal is usually designated by the letters “COM”, the normally closed terminal by the letters “NC”, and the normally open terminal by the letters “NO”. To test the switch:
- Contact the black lead to the common terminal and contact the red lead to the “normally open” terminal.
- Actuate the switch.
- The meter display should indicate “zero” Ohms of resistance.
- Move the red lead to the “normally closed” terminal. The meter display should indicate “zero” Ohms of resistance before the switch is actuated.
If a switch terminal tests positive for continuity when it should not (such as the “normally open”
terminal testing positive before the switch is actuated), then the part has likely shorted closed. This indicates the switch is faulty and will need to be replaced.
Other components, such as electric dryer heater elements, can short as well. When testing for a short, one lead should be touching a terminal or wire while the other lead should contact the outer metal case or cover of the component. If the meter display shows Ohms of resistance, then the component has shorted.
Testing for voltage
A multimeter can also determine if voltage is present and what that voltage is:
- Set the meter for alternating current (AC), used in most homes, or direct current (DC), used for batteries found in cars, lawn mowers, and many cordless products.
- Set the meter dial to the appropriate range above the expected result (example: “200 volts” when testing a standard 120 volt wall outlet).
- Contact the multimeter leads to the power source (a wall outlet or power cord), or at the load (an element or motor). Use extreme caution when testing – avoid touching the metal ends of the multimeter leads or the terminals with your fingers to prevent electrical shock.
- The multimeter display should indicate what voltage is present. If a component is not receiving the correct voltage, then the component is most likely not the source of the problem.
As noted above, most wall outlets in North America provide 120 volts of alternating current. However, some appliances, such as electric dryers and ranges require 240 volts of alternating current to function. The outlets these appliances are plugged into will provide two legs of voltage, each carrying 120 volts. When testing a 240 volt outlet, each outlet slot should provide close to 120 volts and 240 volts when combined, although readings can vary.
Be aware that an alternating current circuit (such as a wall outlet) uses alternating polarity, so the multimeter leads can be reversed without affecting the voltage reading. The same is not true when testing a direct current circuit (such as a car battery) which has constant polarity. If testing a direct current circuit, the positive lead needs to contact the positive terminal and the negative lead needs to contact the negative terminal; otherwise, you could end up with a negative reading.
Using a multimeter to measure resistance
Using a multimeter to test the resistance of a component can tell you if the part is within factory specifications and functioning normally. Every component that draws current has some level of resistance including motors, heating elements, and water inlet valves. Typically, a part that is designed to create heat (like a heating element) will have less resistance than motor windings or valve coils. Control boards will often use a thermistor or sensor which have a resistance value that changes when the temperature inside the appliance rises or falls.
When testing for resistance, the component will need to be isolated from the circuit; otherwise, other components in that circuit could affect the reading. You should not attempt to measure resistance on a live circuit.
If you are unsure where to set the meter range dial, we recommend starting at the lowest setting (example: “200 Ohms of resistance”). You can then move the dial to progressively higher settings for Ohms of resistance as necessary.
Find a multimeter and the replacement parts you need at Repair Clinic
In addition to stocking millions of original manufacturer replacements parts for appliances, outdoor power equipment, and heating and cooling products, Repair Clinic.com also has multimeters available to help you make sure you’re fixing your product right the first time. Be sure to check out Repair Clinic’s numerous “Part Testing” videos to learn how to use a multimeter to properly test fuses, switches, sensors, heating elements, capacitors, solenoid coils, and much more.