How A Dehumidifier Works

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You’ve heard it said (and you may have even said it yourself): the high temperature isn’t so bad because it’s a “dry heat”. During the hottest days of summer, the heat may be tolerable as long as it’s not accompanied by high humidity which has a way of making hot weather feel downright oppressive. That’s why many of us rely on dehumidifiers to keep our homes comfortable. How this unique appliance works and how it can malfunction is what we’ll address in this article.

The basics of dehumidifier operation

Dehumidifiers reduce the humidity level in the room air by drawing that air through the appliance and removing the moisture from it. The level of humidity reduction is regulated by a humidistat or by a control board with a sensor attached, depending on the dehumidifier model. When the humidistat or the sensor detects a need to reduce the moisture in the air, 120 volts of alternating current is sent to the dehumidifier’s compressor and fan motor.

Similar to how a compressor is used in an air conditioner or refrigerator, the dehumidifier’s compressor is part of a sealed refrigerant system that compresses the refrigerant in gas form and pumps it through a set of condenser coils where the gas becomes a hot liquid. The coils dissipate the heat as the liquid travels through them. Once the refrigerant has passed through the condenser coils and a capillary tube, it travels to a set of evaporator coils. As the refrigerant liquid enters these coils, it expands into a gas which makes the coils cold. The refrigerant gas will then flow through the evaporator coils to a suction line attached to the compressor. The compressor will then pump the gas back into the condenser coils, where it once again becomes a hot liquid, and the cycle continues.

At the same time, the dehumidifier’s fan motor rotates a fan blade to draw the humid air into the appliance where it condenses on the cold evaporator coils. The condensation accumulates on the evaporator and drips into a bucket or is diverted through a hose to a floor drain. The cooler air from the evaporator is heated as it passes through the condenser coils and this dryer air is returned to the room. This process continues until enough moisture has been removed from the air to satisfy the setting on the humidistat or control board.

Keep the dehumidifier coils and air filter clean

Both the condenser and evaporator coils require proper air flow for the dehumidifier to operate efficiently. Over time, these coils can collect dust, dirt, and debris, so it’s a good idea to clean the coils regularly. You can use a long brush to do this – just be careful not to bend the condenser or evaporator coil fins when brushing away the debris. If the dehumidifier model is equipped with an air filter, the filter will need to be cleaned periodically to prevent frost from building up on the evaporator coils.

Maintain an appropriate room temperature for optimal dehumidifier operation

Be aware that most standard dehumidifier models require the room temperature to remain above 65° Fahrenheit (18° Celsius) for the appliance to work properly as lower temperatures can cause those evaporator coils to frost over. If you prefer keeping the temperature in your home lower than 65° Fahrenheit, you will want to obtain a dehumidifier that is specifically designed for lower temperature operation such as a Honeywell 70 Pint Energy Start Dehumidifier or a Frigidaire High Humidity 50 Pint Dehumidifier.

Troubleshooting a malfunctioning dehumidifier

Is your humidifier not working as good as it used to or is it failing to work at all? Repair has identified the five most likely causes you should investigate as part of the troubleshooting process:

  1. Faulty bucket switch – On dehumidifier models that use a water bucket to collect the condensation, a bucket switch will be actuated to shut off power to the dehumidifier when the bucket reaches capacity. If the switch fails in the “open” position, it will prevent the dehumidifier from running. To determine if the bucket switch is faulty, you can use a multimeter to test the switch for electrical continuity – a continuous electrical path present in the switch. If the switch tests negative for continuity in the “open” position (before the switch is actuated by a filled water bucket), you’ll know the part is defective and will need to be replaced.
  2. Defective humidistat or humidity sensor – When the level of moisture in the air is too high, the contacts in the humidistat or humidity sensor close to allow the dehumidifier to run. If the contacts fail to close, the dehumidifier won’t work. As with a bucket switch, you can use a multimeter to test the humidistat or sensor for electrical continuity, provided the area you’re testing the component in has high humidity. TIP: Run a hot shower in the bathroom for a while to build up humidity then test the humidistat or sensor in the bathroom.
  3. Malfunctioning control board – The dehumidifier control board reacts to the contacts closing in the humidistat or humidity sensor by allowing voltage to reach the fan motor to draw in the moist air. If the control board is malfunctioning, it may not allow the fan motor to turn on. While you cannot easily test the control board, you can inspect it for signs of burning or a shorted-out component.
  4. Faulty compressor – The compressor is the component that keeps the refrigerant pumping through the dehumidifier’s condenser and evaporator coils. Although it’s not a common problem, a faulty compressor can fail to adequately draw the refrigerant through the coils which will result in the dehumidifier being unable to remove the moisture from the air. Before you consider having the compressor replaced, you should inspect all other dehumidifier components first. To help determine if the compressor has failed, you can use a multimeter to test for continuity between the electrical pins on the side of the compressor. If there is an open circuit, the compressor is likely defective. Due to the complexity of correctly installing a new compressor and introducing new refrigerant, this job should be handled by a licensed technician.
  5. Incoming power problem – There’s always a chance that the dehumidifier components are all in good condition, but the appliance simply isn’t receiving enough current to work. You should set a multimeter to “Volts AC” and test the electrical outlet the dehumidifier’s power cord is plugged into to determine if it’s providing close to 120 volts. Of course, if the outlet is not providing any voltage at all, check to see if a home circuit breaker has tripped or a fuse has blown.

Finding the right dehumidifier part with help from Repair Clinic

Whether you own a Frigidaire, GE, Goldstar, Haier, Honeywell, LG, Whirlpool, or any other name-brand dehumidifier, Repair can help you find the right replacement part to get your appliance back in good working order. To get started, enter the full model number of the dehumidifier in Repair Clinic’s “Shop Parts & Get Answers” search bar to reveal a comprehensive list of parts compatible with that particular model. Next, use the “Part Category” and “Part Title” navigation filters to narrow the list down to find the exact fan motor, bucket switch, humidity sensor, humidistat, control board, or air filter you need.

As your repair partner, Repair Clinic not only stocks genuine OEM replacement parts, but this one-stop online resource has an in-depth collection of “Repair Help” material that puts the knowledge in your hands. Explore thousands of troubleshooting and step-by-step procedural videos, articles, diagrams, and schematics to learn how to fix and maintain all major home appliances, outdoor power equipment, and heating and cooling systems. Supporting do-it-yourselfers and professional technicians alike, Repair Clinic will save you time and money on every repair.

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