How to Defrost a Dehumidifier

High relative humidity can cause a variety of problems in your home. At best, it may be uncomfortable, and at worst, it can lead to the propagation of mold and other organisms harmful to your health and damaging to your belongings. To prevent these problems, strict humidity control is essential. If you live in an area with high humidity, a dehumidifier can be a beneficial investment.

After choosing the best dehumidifier model for your space, it will also take some time and effort to keep your dehumidifier functioning properly for a long time. However, even if you do everything to maintain your dehumidifier well, there may be some unavoidable issues due to natural wear and tear and extreme weather conditions. For example, when temperatures drop during colder months, you might notice some frost forming inside your dehumidifier.

In most cases, frost on your dehumidifier coils is simply because of low ambient temperatures. Most dehumidifiers will defrost automatically when this happens. If frost forms and your dehumidifier doesn’t defrost automatically, there are a few simple steps you can follow to solve the problem. Although, for more severe problems, it’s always best to get help from a licensed HVAC technician or contact the manufacturer.

How Your Dehumidifier Works

Before you can solve any of its problems, you must first understand how your dehumidifier works to be able to tell when it’s functioning properly.

Dehumidifiers work to reduce moisture in the air using different methods of moisture removal. The two main types of dehumidifiers are classified by the dehumidification method they use: refrigerant and desiccant. Probably what most are familiar with, however, is the refrigerant dehumidifier. The main process is similar to that of an air conditioner and other appliances that use a compressor. 

The compressor pumps the refrigerant to and from the condenser and evaporator coils to facilitate the cooling system. First, a fan draws the warm and moist air into the dehumidifier and passes it over the cold evaporator coils. As the air temperature decreases, the air loses hold of the water vapor, resulting in condensation. The dry air is now released back into the room. Water droplets drip down into the tank or flow out through the drain hose. 

Since it relies on the condensation of moisture, this type of dehumidifier performs well only in warm and humid conditions. Most refrigerant dehumidifiers are limited to temperatures as low as 41°F, while the efficiency starts to decrease at 65°F. Instead of cooling down the air, it could end up freezing the condensate on the dehumidifier coils. These dehumidifiers typically include defrost mode to prevent ice buildup.

Refrigerant Flow Chart

The other type of dehumidifier uses a desiccant substance to extract excess moisture in the air through a process of absorption or adsorption. Rather than cooling the air down to its dew point, the desiccant binds with the water molecules chemically. Depending on the type of desiccant, it can either be renewed and reused repeatedly or simply disposed of after one use. This type of dehumidifier has low risks of frost and thus works best in low temperatures. However, it usually has a much lower capacity and higher consumption than the equivalent refrigerant dehumidifier.

Why Does a Dehumidifier Freeze Up?

In addition to a short term solution, if it’s happening regularly you need to identify why your dehumidifier keeps freezing up. Then you can also prevent it from happening again.

Low Temperature

As mentioned, most refrigerant dehumidifiers do not work well in low temperatures. Perhaps the most common reason for a dehumidifier to freeze is simply that the ambient temperature is too low. Once the temperature drops to 65°F or lower, frost may start to form on the coils. Since the dehumidifier needs to cool down the air, the moisture may freeze on the coils instead. Most dehumidifiers have the function to defrost automatically when it senses frost on the coils. In defrost mode, the compressor will stop while the fan keeps running to melt the ice. 

Broken Temperature

Broken Temperature Sensor

When the ambient temperature reaches past the dehumidifier’s operating temperature range, the unit should stop working. Dehumidifiers have a humidity or temperature sensor to tell when it needs to stop and defrost. However, if this sensor is broken, the dehumidifier may keep running nonstop even in lower temperatures, causing ice to build up. Furthermore, a faulty humidity sensor may also cause the unit to keep working even when your set humidity level is already achieved.

Blocked Airflow

When frost forms on the evaporator and condenser coils and the dehumidifier does not activate auto defrost, then ice may build up, which can damage the coils and other internal components. However, if the defrost mode is working but the airflow is blocked, the fan may not be able to melt the ice completely, causing it to build up inside. The airflow may be blocked due to wrong placement or if the dehumidifier is too close to walls, furniture, or other items.

Clogged Air Filter

The humid air first passes through the filter before entering the refrigerant system. This reduces particles in the air and protects the internal components of your dehumidifier. If the air filter is clogged with dust, dirt, and other impurities, it can restrict airflow to the unit. Thus, the fan may not have enough power to melt the ice, allowing frost buildup. Filter cleaning is routine maintenance and many dehumidifiers include an indicator light to remind you to clean the filter after a certain amount of time.

Dirty Coils

Dust and dirt can also get on the evaporator coil, which can affect the cooling system. The evaporator coils need to cool down the air and if it’s all clogged up, it can get too cold and lead to frost buildup That’s why you must clean the air filter regularly to protect the coils and other components from dust and dirt.

Dirty or Broken Fan

If the dehumidifier is turned on but the fan is not working properly, this can also limit air circulation and lead to the cold coil icing up. If there are no blockages and the air filter is clean, but there is limited airflow, check if the fan is dirty. Once you clean the fan blade but there’s still no airflow, it might be broken and need to be replaced. If there’s nothing wrong with the fan itself, then you may be dealing with a faulty fan motor or blower wheel. Check if there are any loose screws and tighten them. Otherwise, you may need to replace the broken fan motor. 

Other Mechanical or Electrical Failures

Operating your dehumidifier in less than ideal conditions can overheat the compressor circuit. This, on top of other possible electronic malfunction or faulty wirings, can lead to ice buildup inside your dehumidifier. This can be hard to tell on your own, so it’s recommended to ask a professional technician or contact your manufacturer.

How To Fix A Dehumidifier Freezing Up

Before you spend anything, here are some ways you can check and try to solve the problem with your dehumidifier.

First and foremost, check the temperature on the display if it’s available, or on a separate device. Note that most refrigerant dehumidifiers stop working at 41°F and frost may start to form at 60°F. If your dehumidifier is functioning properly, it should activate auto defrost and melt the ice before resuming normal operation. If you notice frost but the unit does not defrost, just turn it off and defrost it by operating in fan mode or using a separate fan to melt the ice. 

If the unit is taking too long to defrost, check if there is any blockage to its air circulation. Keep the unit away from walls and other items and close all windows and doors for proper circulation inside the room. If you hear any unusual sound from the fan, you may need to clean it.

Check the filter and clean it regularly to prevent clogging up the air with dust, dirt, and other impurities. Wash the filter in running water or soak it in warm soapy water to remove any remaining dirt. Let the filter dry completely before placing it back into the dehumidifier. If the filter is damaged, you need to replace it. For more instructions on filter cleaning or replacement, check your manual.

Cleaning the coils is also essential in maintaining proper functioning and preventing ice buildup. You can do this by using a vacuum cleaner with a brush attachment. However, before doing so, check the manual for specific guidelines. If you are unsure how to do it, leave this task to a professional.

Check the dehumidifier’s temperature sensor. If it’s broken, the digital screen may display an error code with troubleshooting instructions in the manual. If there is no error code and you don’t know how else to proceed, do not attempt to disassemble any parts. Call a licensed technician to get your dehumidifier checked.

Most importantly, try not to run your unit in low temperatures. Cold air is usually low in humidity anyway. Always check the indoor temperature and humidity to know if you even need to use a dehumidifier. When using your dehumidifier, make sure to keep it away from walls and other items to let the air flow properly.


How long does it take for a dehumidifier to defrost?

Normally, a dehumidifier should be able to finish a defrost cycle within an hour or so. However, it varies depending on the ambient temperature. If it’s below 60°F, the unit may spend more time defrosting than actually dehumidifying.

What should I set my dehumidifier at?

Remember that the ideal relative humidity range is from 30% to 50%. For most people, 45% is the best setting to maintain indoor comfort, but it depends on the ambient temperature. When the air is too low, you might need to set the relative humidity level lower.

Should a dehumidifier run constantly? 

No, you do not need to run a dehumidifier all the time, especially in winter. Ideally, you only need to run the unit when the humidity level reaches 60% or higher. Constant dehumidifier use can be wasteful of energy and even become harmful when it dries up the air of all moisture.


Dehumidifiers generally work best in warm and humid environments. Even the best dehumidifiers may work less effectively as the temperature decreases. Refrigerant dehumidifiers may start to form frost when temperatures drop below 65°F. Most have a built-in auto defrost function that senses frost and stops dehumidification for a time to melt the ice. Try not to operate the dehumidifier when the air is too cold. 

If you notice frost inside the unit but auto defrost doesn’t activate, stop running the dehumidifier and perform the troubleshooting steps above after checking your manual. If you’ve inspected everything, cleaned up all the dirt and dust, and you’re still not sure how to solve your problem, call a professional HVAC technician to check your dehumidifier.

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