AC vs DC voltage and how to test both with a multimeter

When your appliance stops working, the first instinct might be to start replacing parts. However, before spending money you don’t need to, it’s better to test the electrical parts to confirm which one is bad. Whether you’re dealing with a dead heating element, a non-responsive control board, or a faulty power cord, checking voltage is an essential troubleshooting step. Many appliance issues come down to a power problem, and using a multimeter to check for voltage is a simple way to diagnose the issue.

The information in this article may not apply to your specific appliance model. We recommend consulting your manufacturer’s documentation or contact us with any questions.

Understanding AC and DC voltage in appliances

All appliances need voltage to run but different parts can rely on either AC (alternating current) or DC (direct current) voltage, depending on their role. Since appliances may use both types of voltage, knowing where and how to measure each type is important when troubleshooting. 

AC voltage (alternating current)

• AC power flows in both directions, switching back and forth in cycles.
• This is the type of electricity supplied by your home’s wall outlets.
• Most large appliances such as ovens, dryers, refrigerators, and washing machines use AC voltage for their main power supply.
• parts like heating elements, motors, and compressors typically run on AC.

DC voltage (direct current)

• DC power flows in only one direction, maintaining a steady voltage level.
• Found in battery-powered devices, electronic circuits, and appliance control boards.
• Many modern appliances convert AC to DC internally to power electronic parts like digital displays, touch controls, and inverter compressors.
• If an appliance has a control board, it likely uses DC voltage for some of its operations.

Why testing voltage matters in appliance repair

Using a multimeter to check voltage can save time and money when troubleshooting an appliance. Instead of guessing which part might be faulty, you can confirm whether a part is receiving power and functioning correctly before replacing it. By testing voltage before replacing parts, you can quickly determine whether an issue is electrical or mechanical. If you confirm a part is faulty, AppliancePartsPros.com can help you find the right OEM replacement.

The benefits of testing 

• Avoids unnecessary part replacements. Sometimes, an appliance issue isn’t caused by a failed part but by a power supply problem. Testing first allows you to replace only what’s truly broken.
• Identifies power supply issues. Checking the voltage at the outlet, power cord, or control board helps determine if the problem is with the appliance itself or if you need to call an electrician.
• Saves time on troubleshooting. Instead of trial-and-error part replacements, testing voltage gives a clear answer about where the problem lies.

Using a multimeter: getting started

There are two main types of multimeters. For appliance repair, a digital multimeter is recommended because it provides quick, clear readings. Analog multimeters with a needle gauge can work well but can be harder to read for precise voltage measurements.

Most multimeters have separate settings for AC and DC voltage:

• AC voltage (V~ or VAC) – used for checking power outlets, power cords, and appliance motors.
• DC voltage (V⎓ or VDC) – used for testing control boards, touch panels, and battery-powered parts.
• Continuity mode (Ω) – used to check if a circuit is complete, often for testing fuses and heating elements.

Before testing any appliance, follow these safety guidelines:

• Always unplug the appliance before testing internal parts.
• Set the multimeter correctly. Using the wrong setting can cause inaccurate readings or damage the meter.
• Hold probes by the insulated handles. Avoid touching metal probe tips while testing.
• Test power at safe points. Avoid exposed wiring and only test at terminals designed for voltage testing.

How to test AC voltage in appliance parts

Many major appliances run on AC voltage, including ovens, dryers, refrigerators, and washing machines. Testing AC voltage with a multimeter can help determine if power is reaching an appliance or a specific part.

Set up the multimeter for AC voltage

1. Turn the dial to AC voltage (V~ or VAC). Some multimeters have multiple AC ranges, so if you’re unsure, start with the highest setting and work down.
2. Insert the probes into the correct ports. The black probe goes into the COM (common) port, and the red probe goes into the V (voltage) port.
3. Confirm the expected voltage range. Most household appliances run on 120V or 240V AC, depending on the device.

Test a power outlet or appliance cord

To check if an appliance is getting power from the wall outlet or power cord:

1. Insert the black probe into the neutral slot of the outlet or touch the neutral wire of the cord.
2. Insert the red probe into the hot slot of the outlet or touch the hot wire of the cord.
3. Read the voltage on the display. A standard U.S. outlet should read about 120V, while larger appliances like dryers and ovens may use 240V.
4. If the reading is significantly lower than expected or zero, the outlet or power cord may be faulty.

Important: when testing inside an appliance, only test live voltage if necessary and comfortable doing so. If possible, unplug the appliance and test continuity instead.

How to test DC voltage in appliance parts

Many modern appliances use DC voltage for control boards, touch panels, and electronic parts. Since these parts often receive power from an AC-to-DC converter, testing DC voltage can help determine if an issue is with the power supply or the part itself.

Setting up the multimeter for DC voltage

1. Turn the dial to DC voltage (V⎓ or VDC) . Some multimeters have multiple ranges, so start with the highest if unsure.
2. Insert the probes into the correct ports. The black probe goes into the COM (common) port, and the red probe goes into the V (voltage) port.
3. Identify the expected voltage range. Common DC voltage levels in appliances include 5V or 12V for control boards and electronic displays, 24V for some appliance relays and actuators and variable DC voltage in inverter compressors and advanced motor systems.

Testing DC voltage in control boards and circuits

Control boards regulate many appliance functions, and if an appliance is unresponsive, checking the board’s DC voltage can help pinpoint the issue.

1. Locate the DC power terminals on the control board. These are usually labeled with voltage ratings.
2. Place the black probe on the negative (-) terminal and the red probe on the positive (+) terminal.
3. Read the voltage on the display – compare it to the expected voltage from the board’s label or wiring diagram.
4. If voltage is present, the issue may be with the board itself; if no voltage is detected, the power supply or wiring may be faulty.

What to do if a part fails a voltage test

If a part doesn’t show the correct voltage or isn’t functioning as expected:

1. Double-check the connections. Loose wires or corroded terminals can cause power issues.
2. Confirm the correct voltage setting on the multimeter. Using the wrong mode can give incorrect readings.
3. Retest at different points in the circuit. Check power at multiple locations to find where the issue starts.

Additional information

Thanks for reading! If you need replacement parts, grab your model number and head to AppliancePartsPros.com. We offer over two million parts and most orders arrive in two business days. If you need help finding the right part or placing an order, you can contact our team at 1 (877) 477-7278.

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