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How to Fix a Dehumidifier

Diagram of Dehumidifier Parts ©

Expert advice on how to repair a dehumidifier that doesn’t work, does a poor job of dehumidifying, or has other problems.

If your dehumidifier doesn’t work right, a simple cleaning of the condenser and evaporator coils may be all that’s necessary to fix it. This article discusses common dehumidifier problems with helpful tips on how to solve them. Please see the list of typical dehumidifier problems top right.[GARD align=”left”]

If your dehumidifier shows no signs of life whatsoever:

1Check the power. Be sure it is plugged into a working outlet and is turned on.

2Unplug the dehumidifier unit and check the power cord. If necessary, replace the cord.

3Remove the cover panel and look for ice. If you see any ice blocking parts, let the ice melt and do not use the unit until the room temperature exceeds 65 degrees Fahrenheit (most dehumidifiers are not designed for use in colder spaces and may freeze up). Many people find that by unplugging the unit and waiting about 30 days into the season the problem is solved.

4Remove and test the overflow cutoff switch. You can do this with a volt-ohm meter. Clip the leads to the terminals on the switch. Depress the bar or trip lever on the switch. If the meter’s needle does not show continuity and also no continuity as the switch is clicked back and forth, the switch is probably faulty and will need to be replaced.

5Remove the humidistat and check it. You can test a dehumidifier’s humidistat fairly easily using a volt-ohm meter. Also using a volt-ohm meter, you can tell if the overflow switch works or not. Just set the meter to the RX1 scale and attach its leads to the humidistat’s terminals. Rotate the humidistat’s knob as far as it will turn in both directions. If the volt-ohm meter registers zero ohms through only part of the humidistat dial’s range, the humidistat is working. If it registers zero through the entire range, it’s broken and must be replaced.

6If the unit still doesn’t work, decide whether you’re better off replacing the appliance or calling a repair person (this decision will depend upon the value of your dehumidifier)—the compressor motor or the relay and overload switch may be the problem.

Dehumidifier Does Not Work Well

If your dehumidifier seems incompetent, it may be undersized for the space. Check the unit’s specifications to be sure it can handle the room size. If you don’t want to replace it with a larger one, try closing doors and dehumidifying the space a section at a time. After disconnecting the power cord, you can also:

1Remove the cover and clean the condenser and evaporator coils.


2Lubricate the fan motor bearings with a couple of drops of oil if the motor has oil ports (some dehumidifiers don’t need to be oiled). While you’re at it, make sure that the condenser isn’t clogged with dust or dirt.

3Finally, make sure your humidistat is functioning properly by testing it with a volt-ohm meter. Just set the meter to RX1 scale and attach its leads to the humidistat’s terminals. Rotate the humidistat’s knob as far as it will turn in both directions. If the volt-ohm meter registers 0 ohms through only part of the humidistat dial’s range, the humidistat is working. If it registers 0 through the entire range, it’s broken and must be replaced.

4If it still operates poorly, call an appliance repair person for advice or take the unit into an appliance repair shop.

Dehumidifier Overflows or Leaks

Many dehumidifiers have a float switch that prevents the unit from spilling over with the water that has been drawn out of the air. Sometimes this switch goes bad and must be replaced. If your dehumidifier is overflowing, you can test the overflow prevention switch with a volt-ohm meter.

1Unplug the dehumidifier and remove the switch.



2Disconnect the leads and clip the leads to the terminals on the switch.


3Check the pan or reservoir and empty it if necessary, or make sure the drain isn’t clogged.


4Straighten any kinks or bends in the unit’s hose.


5Set a volt-ohm meter to the RX1 scale (or to K-Ω or Ω resistance on a digital meter) and depress the bar or trip lever on the switch. If the meter’s needle shows no continuity as the switch is clicked back and forth, the switch is probably faulty and will need replacement.

Dehumidifier Freezes Up

Is your dehumidifier freezing up? If your dehumidifier ices up, it’s important to solve the problem—running a dehumidifier that’s totally iced up can damage the compressor.

A dehumidifier will often frost up if room temperatures are colder than about 65 degrees Fahrenheit. Though some “basement humidifiers” are designed to work in temperatures below 65 degrees F, conventional humidifiers are not.

dehumidifier ices up

Dehumidifier with low-temperature setting operates below 45 degrees F. without icing up.

If your room temperature isn’t overly cold, airflow to the unit may be restricted or blocked, the unit may have a faulty de-icer switch, the refrigerant gas in the unit may be too low, or the compressor may be failing.

To troubleshoot a dehumidifier that freezes up:

1Take a look at your room temperature, as previously stated. If the room temperature is lower than 40 degrees F., the dehumidifier will definitely freeze up. A clear indicator of this is an evaporator coil that is frosted up completely and evenly (see Step 5 for information on opening the unit). If you suspect that your room temperature may be too cold, try setting the dehumidifier on a table so that it circulates slightly warmer air. You can also try aiming a small blower or heater at the unit—if this solves the problem, consider raising the room temperature slightly.

2Be sure the unit is set far enough from the wall so that airflow isn’t restricted. Anything that prevents room air from freely moving through the unit can cause the dehumidifier to freeze up. (However, do not place it in a drafty spot.)

3Be sure the fan is working. If you don’t hear the fan blowing air across the coils when the unit is turned on and supposed to be operating, the dehumidifier will freeze up.

4Clean the filter if it has one. If your dehumidifier has a filter, follow the manufacturer’s instructions to clean it. In most cases, you use a vacuum cleaner to do this; foam filters can be cleaned with spray from a faucet.

5Vacuum the condenser coils. If the coils inside the unit are dirty, they cannot operate efficiently. Unplug the dehumidifier and open it up by removing the screws that secure the outer cover. Note whether the coils are completely iced up or only partially iced up. If only certain sections of the coils are iced up, the problem is likely to be caused by low refrigerant or a failing compressor (see Step 8). Allow all ice to melt and excess moisture to evaporate from the coils. Then, using a brush attachment on a vacuum cleaner, remove all dust buildup, being careful not to damage the coils.

6If vacuuming the coils doesn’t do a good enough job of getting them clean, take the unit outside, cover the motor and electrical parts with plastic sheeting, and spray the coils with water. Drain the unit and allow it to dry completely before putting it back together and plugging it in.

7Test the unit. After plugging the dehumidifier in, turn it on to see if it freezes up again.


8Make a decision. If it still doesn’t work, it is probably low in refrigerant. Now you have to make a decision to either take it into an appliance repair shop or toss it and buy a new one. Before taking your dehumidifier into a repair shop, get a phone estimate of the cost of recharging and/or repairing it. Then evaluate whether or not it’s worth doing. If you decide to buy a new one, please see the free Dehumidifiers Buying Guide.

Dehumidifier Smells Bad

Does your dehumidifier smell bad? If your dehumidifier stinks or smells musty or like sulfur or mold, this expert advice will help you troubleshoot and solve the problem.

Dehumidifier odors are generally caused by stagnant water that has pooled in a hose or by chronically dirty condenser coils. Though you might be tempted to clean it with some type of disinfectant or household cleaner, resist the temptation! You should not use any type of chemicals in a dehumidifier—the residue is too difficult to remove and some chemicals can be caustic. Instead, use vinegar (its smell with be strong at first but will dissipate with time), hydrogen peroxide to clean the reservoir, coils, and filter. Use these two non-toxic chemicals in sequence, applying and removing the vinegar first, and then the hydrogen peroxide, which helps remove the vinegar’s odor.

How to Clean a Dehumidifier

After unplugging the dehumidifier, take it outside to work on it. Here’s how to clean it to rid it of odors:

1Fill one spray bottle with full-strength white vinegar and another spray bottle with full-strength hydrogen peroxide.

2Clean the reservoir / drip pan. Start by completely emptying it and mopping up any damp areas. Then spray the inside of the reservoir /drip pan with vinegar, allow to sit for 10 minutes, and then rinse thoroughly with clear water. Use a clean rag or new sponge to wipe it out and repeat the rinse and wipe process. Follow up with the hydrogen peroxide, following the same methods.

3Clean the coils with a brush and a garden hose. Then spray them with vinegar and allow to sit for 10 minutes. Rinse thoroughly with water, wipe clean, and repeat with hydrogen peroxide. Allow the unit to dry in a warm place for at least 24 hours.

4Clean the filter. To clean a dehumidifier filter, remove it and spray it with vinegar. Allow this to sit for 10 minutes, then rinse it thoroughly and spray it with hydrogen peroxide. Let this sit for 10 minutes, rinse again, and wipe it clean with a clean cloth or new sponge.

5Wipe the fan blades clean. Remove the cover first, then use a damp cloth to clean the fan blades and the area around the motor.

Put two teaspoons of baking soda in the dehumidifier’s tank to prevent future mildew and mold odors. In the future, empty the dehumidifier regularly so that it doesn’t have time to grow mold or bacteria.

Dehumidifier Is Noisy

Is your dehumidifier making strange noises? If it is, the noises are probably caused by loose, vibrating parts. After disconnecting the power:[GARD align=”right”]

1Remove the cover and look for loose screws or vibrating parts and check to see if the rubber compressor mounts have hardened so that they no longer absorb the unit’s movement. If they have, replace them.

2Wiggle the fan to see if it is loose on its shaft. If it is, tighten the mounting fasteners. Lubricate the motor’s bearings if suggested by your owner’s manual.

3If it still makes noise, call an appliance repair person or take the unit into an appliance-repair shop.

How a Dehumidifier Works

If your home doesn’t have air conditioning, it may rely upon a dehumidifier to reduce uncomfortable, muggy humidity in room air. A dehumidifier uses refrigeration principles the way an air conditioner does, but it doesn’t cool the air—in fact, it warms it slightly.

A dehumidifier is a box that contains cold evaporator coils, warm condenser coils, a fan, and a reservoir or drain to catch water. The fan blows moisture-laden room air over the cold coils, where water condenses and drips into the pan or drain. The drier air then blows across the warm coils and back into the room.

Although a dehumidifier does not cool the air, it makes it more comfortable because it decreases the humidity. But a dehumidifier does not function well under about 65 degrees F.

A dehumidifier’s fan must have electric power, the evaporator coils must contain a proper charge of refrigerant, and the controls must work for the dehumidifier to operate.[GARD align=”left”]

In the same way that a thermostat controls a heater or air conditioner, a dehumidifier is cycled off and on by a humidistat that measures a room’s humidity.

NEXT SEE: Dehumidifiers Buying Guide

Dehumidifiers Buying Guide

This expert, unbiased buying guide will help you chooses the right dehumidifier for your home. Includes information on solving humidity problems and selecting between portable and whole-house dehumidifiers.

Room-size dehumidifier protects against excessive moisture problems. Photo: Frigidaire

If your home is stuffy or musty, and water condenses on windows and pipes, it is showing signs of humidity levels that are too high. Showering, running a washing machine or dishwasher, cooking—all of these activities put moisture into the air, which can be problematic, especially if you live in a climate where humidity levels are already uncomfortably high.

Balanced humidity inside a house is important not only for your family’s optimal health and comfort but also for the house itself. When the humidity level—the amount of water vapor in the air—rises too high or drops too low, a variety of problems can develop. This article is about dealing with high humidity; for information on handling low humidity, please see Humidifiers.

Solving Too High Humidity

High humidity can be a problem during both winter and summer. During winter, the first sign of overly humid air is condensation forming on the inner surfaces of windows, encouraging mold and mildew. Though this normally isn’t a serious problem, the same condensation may collect on the inner surfaces of exterior walls unless the walls are fitted with a proper vapor retarder. This can rot the structure and ruin insulation. Peeling, blistering, or cracking paint on siding—especially if bare siding is visible in spots—usually indicates this condition.[GARD align=”left”]

Too-high humidity in the summer is just plain uncomfortable. When room air is humid, the natural cooling evaporation of moisture from your skin is slowed down and, as a result, you feel hot and “sticky.”

Sometimes humidity can be reduced to an acceptable level simply by using kitchen and bathroom exhaust fans. Other methods include making sure the clothes dryer is vented outdoors (for safety, a gas dryer absolutely should be!), keeping showers short, and running only full loads in washing machines and dishwashers. Also eliminate sources of leaks or standing water in the basement or crawlspace. But when you’ve tried these measures and they’re not enough, it’s time to turn to mechanical assistance.

On sultry summer days, when indoor humidity rises above the comfort range, the easiest way to solve high humidity is to turn on air conditioners. Then again, if your home isn’t equipped with AC or the weather is too cold for AC, a dehumidifier may be necessary for drying the air.

Choosing the Best Dehumidifier

Dehumidifiers are a practical and easy solution for reducing high humidity levels. A dehumidifier is a relatively simple appliance that is designed to extract excess moisture from indoor air, making interior spaces far more comfortable and healthy for occupants.

When buying a new dehumidifier, the first decision is the size of the unit needed. For significant, perennial issues of high humidity, you may want to opt for a central whole-house dehumidifier that uses your home’s heating-and-cooling system to reduce the humidity throughout your entire house. Then again, if high humidity is only periodic and in localized areas of your house, such as a basement, a portable dehumidifier that serves a single area will do the job.

After choosing the size of unit, you’ll need to select a technology—dehumidifiers use any of several principles for removing moisture from air. For more about this, please see How a Dehumidifier Works.

Portable Dehumidifiers

Portable dehumidifiers, which you simply plug in, are the most popular models for homes that have just periodic, localized issues with moisture. They are available at big box hardware stores and major home improvement centers. Advances in technology have made these dehumidifiers easy to use, affordable, and effective at improving a home’s air quality. The goal is to choose one that s efficient and effective at reducing indoor humidity and keeping it at optimal levels.

Small portable dehumidifier is helpful for humidifying a single room. Photo: Honeywell

Portable dehumidifiers differ in a variety of ways. Following are some suggestions for choosing one that will function optimally in your home.

Dehumidifier Size

Pick a dehumidifier to fit the space where it will operate. To get a properly sized dehumidifier, you need to know the square footage of the room you want to dehumidify and have a general idea of the area’s moisture levels. A dehumidifier’s drying capacity is measured by how many pints of water it can remove from the air in 24 hours.[GARD align=”left”]

The Association of Home Appliance Manufacturers (AHAM) sets the standards for sizing dehumidifiers to match a homeowner’s needs. Most manufacturers print an easy-to-follow sizing chart on the packaging of their dehumidifiers to help you pick the right size for the space. If you do not see a sizing chart with the model you are considering buying, ask a sales clerk for the AHAM Selection Guide.

You are better off buying a higher capacity dehumidifier than a unit that is too small. Smaller units may run continuously without bringing the humidity down to optimal levels. Higher capacity humidifiers also can handle spaces that may be excessively damp from clothes dryers or dishwashers, which add moisture to the air. Also, if the outdoor climate is humid, it will increase indoor humidity levels. If you live in a humid region, you may want to choose a higher capacity dehumidifier than what the square footage of the room indicates.

Humidity Control

Choose a humidifier with automated controls for monitoring and setting relative humidity levels. The optimal relative humidity in a home should be between 40% and 50% in summer and 30% and 50% in winter. Dehumidifiers with built-in hygrometers measure relative humidity and display the number. An adjustable humidistat allows you to dial a desired humidity level and the unit will automatically maintain it.

If the dehumidifier you choose does not have these settings, you may want to invest in a hygrometer to hang next to the dehumidifier. The device ranges in price from $10 to $60 and will measure the indoor humidity so you know when to switch the unit on and off.

Large console humidifier can handle large areas and multiple rooms. Photo: Bemis

Water Capacity

Consider the unit’s bucket size. Dehumidifiers with larger tubs or drip pans need to be emptied less often. But expect to pay a little more for the convenience. A rule of thumb is that the more water a dehumidifier can extract and hold, the more it is likely to cost. Shop around because prices can vary. Expect to pay about $140 for a 25-pint dehumidifier and $225 for a 70-pint dehumidifier. Dehumidifiers with front-loading buckets are easiest to empty.

Most portable dehumidifiers are equipped to be self-draining and come with a drain-hose connection. But the dehumidifier will need to be placed in an area where the hose can empty water, such as into a basement floor drain or a laundry room sink.

Defrost Features

Opt for a dehumidifier that can function at low temperatures. Unless you live in a climate that is warm year-round, consider a unit with an automatic defrost feature. The heat-exchange coils on a dehumidifier can frost over when indoor temperatures drop below 65 to 60 degrees F. so look for a unit that is Energy Star certified to 45 to 40 degrees. Although you may pay a little more for the automatic defrost feature, it will spare you the expense of replacing a unit damaged from iced coils.

Quiet Operation

Noise can be a nuisance, especially if the dehumidifier is in or near a bedroom. Dehumidifiers with two-speed fans run quietly at lower humidity levels. They also save on energy costs. It’s not a bad idea to test a dehumidifier’s noise level before you make your purchase.


Make sure your new dehumidifier comes with casters so it can be rolled from room to room. A long power cord will enable you to put the unit anywhere you want it.[GARD align=”right”]

Automatic Shutoff

An overflow protection valve will cause the unit to switch off when the tub is full and needs to be emptied. This is a key feature to have on any model you choose. Some dehumidifiers have indicator lights to show when the bucket is full.

Energy Efficiency

Dehumidifiers that carry the Energy Star label will save money on utility bills. Dehumidifiers certified with the government-sponsored label are guaranteed to use less energy yet run efficiently.

Washable Filters

Some models have filters that protect the coils from dirt and dust. Make sure you can easily remove the filters and wash them, a task you should do about twice a month. This will allow you to replace the filters less often.

Whole House Dehumidifiers

Whole house dehumidifiers are the most expensive models, costing between $1,000 and $2,000. They typically are fixed units professionally installed and connected to existing ductwork in a home’s central air or heating system (often right at the furnace or air-handler cabinet). There are three common types of home dehumidifiers: heat pump dehumidifiers, chemical absorbent dehumidifiers, and dehumidifying ventilators. Each has its advantages and disadvantages.

Whole-house dehumidifier is designed to be attached to the home

Heat pump dehumidifiers extract water from the air by using a heat pump that is similar to an air conditioner pump. First, a fan pulls the indoor air across a very cold coil, which causes the moisture to condense. The droplets drip into a bucket inside the unit or are pumped to a drain through a hose. The dry air is warmed by a second, heated coil and exhausted at room temperature. These dehumidifiers are considered among the most effective.

Chemical absorbent dehumidifiers work best in warm climates. They use a chemical drying agent, or desiccant, on a heat exchange wheel to absorb water molecules from the air. Damp air is sent outside via vents. Desiccant dehumidifiers use a lot of energy. They are more commonly used by industries than homeowners.

Dehumidifying ventilators have a sensor controller and exhaust fan. The sensor controller activates the unit when humidity reaches a specified level. Dehumidifying ventilators are less effective in muggy climates because they draw outside air into the house. These dehumidifiers often are used in basements. But they can depressurize a room and cause gas spillage. Make sure gas furnaces are properly vented.



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