How To Test A Dryer’s Moisture Sensor

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Both gas and electric dryers are supposed to thoroughly dry an average load of laundry in about 60 minutes. If you’re noticing that the dryer seems to be shutting off prematurely or are dismayed to find your clothes, towels, or linens still wet when the cycle is finished, the cause could be related to a very simple dryer part: the moisture sensor.

Repair Clinic has an easy troubleshooting step you can do to ensure the moisture sensor is working its best and a way you can test the sensor to confirm it’s working at all. But, first, a little background on how that dryer moisture sensor is supposed to work.

How a moisture sensor affects dryer operation

A dryer moisture sensor is a component that measures the level of moisture or humidity inside the dryer drum. The sensor affects dryer operation by determining when the laundry inside the dryer is sufficiently dry and to signal the appliance to stop the drying cycle. While the location and exact implementation of a moisture sensor may vary depending on the dryer model, the underlying principle of how it works is generally the same.

The moisture sensor is typically located on the lint filter housing grille or rear bulkhead

A dryer moisture sensor, a pair of metallic bars mounted in a plastic housing, is typically located on the appliance’s lint filter housing grille or on the rear bulkhead. This is so the tumbling clothes, towels, or linens inside the dryer drum will readily come into contact with the sensor during the drying process.

Wet clothes conduct electricity better than dry clothes

The moisture sensor relies on the fact that wet clothes conduct electricity better than dry clothes. When wet clothes come into contact with the sensor, they create a conductive path between the two sensor elements (the metallic bars). The moisture sensor periodically sends a small electrical current across its sensor elements. If the clothes are wet, the current will flow through the clothes, completing the circuit and allowing the electricity to pass through.

The moisture sensor measures the resistance of the electrical circuit

The moisture sensor measures the resistance of the electrical circuit formed by the wet clothes and the sensor elements. Wet clothes have lower resistance, as they provide a better conductive path, whereas dry clothes have higher resistance. The moisture sensor compares the measured resistance to a predetermined threshold value. The threshold represents the desired moisture level in the clothes. If the resistance is above the threshold, it indicates that the clothes are dry or nearing dryness, and the drying cycle can be stopped.

The sensor assists the control in determining if the drying cycle should continue or stop

Based on the moisture sensor’s readings, the dryer’s control system determines whether to continue the drying cycle or to stop it. If the measured resistance falls below the threshold, indicating that the laundry is still wet, the dryer will continue the drying process. However, if the resistance remains above the threshold, the dryer will stop the cycle, assuming the laundry is sufficiently dry. By using a moisture sensor, the dryer can automatically adjust the drying time based on the actual moisture content of the laundry. This ensures the clothes, towels, or linens are adequately dried, but it also helps prevent over-drying, which can damage the fabric and waste energy.

What happens when a moisture sensor malfunctions

Have you been finding the laundry is not drying efficiently? The moisture sensor may be unable to accurately detect the amount of moisture in the load. This can happen when residue builds up on the sensor bars, something that can happen over time if dryer sheets are used regularly to eliminate static cling and add a fresh scent. One or both of the sensor bars could be broken as well, or a wire connection could be damaged or loose.

If the dryer isn’t stopping when expected, it’s possible the sensor bars have shorted by coming into contact with each other. There is a simple test you can perform using a multimeter that will help you troubleshoot a moisture sensor to determine if the part is malfunctioning or not.

Testing a dryer moisture sensor

You won’t need the dryer to be running to perform the test, so make sure the appliance is turned off and there’s no laundry in the drum. Now, here’s how you can test the moisture sensor:

  • Set the multimeter’s range selection dial to the highest setting for ohms of resistance (the high setting is required to get an electrical continuity reading for most moisture sensors).
  • Contact the black meter lead to one of the sensor bars and the red lead to the other bar. If the meter display shows that ohms of resistance are present, you’ll know the sensor has shorted and the component will need to be replaced.
  • Keeping the meter leads on the bars, apply a wet cloth across both bars. The meter display should show the ohms of resistance changing if the sensor is working properly since the wet cloth allows electricity to be conducted between the bars.
  • If the ohms of resistance do not change after applying the wet cloth, it’s possible the bars have become coated with dryer sheet residue and are unable to accurately detect the moisture. Clean the bars with a light vinegar solution and repeat the test. If the ohms of resistance still do not change, you will likely need to replace one or both of the sensor bars, or the entire moisture sensor assembly.
Dryer Moisture Sensor Testing

More dryer repair help from Repair Clinic

Need to know the correct way to install a new moisture sensor on an LG electric dryer (model DLEX4000B)? What about replacing a single moisture sensor bar on the model DV405ETPAWR Samsung electric dryer? Repair Clinic has model-specific part replacement videos to take you through the entire procedure step-by-step. You’ll find these, plus hundreds of other gas and electric dryer repair videos, guides, and schematics in the “Videos & Articles” section of the Repair Clinic website. This is another way Repair Clinic supports technicians and DIYers alike with the necessary know-how to repair all major home appliances, outdoor power equipment, and heating and cooling systems.

Repair Clinic has the right moisture sensor for your dryer

Once you know how to replace that moisture sensor, you’re going to want to make sure you’re installing the right sensor that’s compatible with the dryer model. Repair Clinic makes this part easy. Just enter the full model number of the dryer in the Repair Clinic website search bar, choose “Sensor & Thermistor” using the “Part Category” navigation filter followed by “Moisture Sensor” using the “Part Title” navigation filter. You’ll be shown the exact original manufacturer equipment moisture sensor that works with the dryer you’re fixing, including those built by Whirlpool, Electrolux, Kenmore, GE, Maytag, LG, and Samsung. With Repair Clinic as your repair partner, you’ll save both time and money with every repair.

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