My Dehumidifier Ices Up - Why?

Why is it a dehumidifier ices up? This question is asked so often and like so many "simple" questions there is no simple answer.

There are several types of dehumidifier each of which reduces relative humidity in a different way. Here we are talking about the type most often found in our homes, the refrigerant type.

If you have a Frigidaire or a Danby, a Kenmore or a Haier or any one of a dozen brands, you have a refrigerant dehumidifier. A refrigerant unit is rather like a refrigerator. It has a compressor, condenser and evaporator coils, and a fan. The compressor and the coils are a refrigeration unit and moisture is condensed onto the cold evaporator coil.

I know it looks as if I've got that the wrong way round but the evaporator coil becomes cold because the condensed, compressed refrigerant evaporates very quickly in the evaporator coil and absorbs heat as it does so. This is how the coil is cooled to such a low temperature that water vapor condenses to liquid water on its surface.

The fan is there to draw moist air from the room into the appliance and to blow the dried air out again.

So, it's not so surprising that a dehumidifier ices up. When it's working properly a thin film of ice will appear on the evaporator coil, even at temperatures as high as 70°F (21°C). As the temperature falls more ice will form and the appliance will stop working from time to time to allow the ice to melt. You may not notice it has stopped unless you see a light glowing with the word "defrosting" on the control panel. This is because the fan keeps running, only the compressor stops working.

If it spends more time defrosting than it does working your dehumidifier ices up because the place where you use it is too cold for a standard model to operate. You could try raising it a few feet, the air nearer the ceiling is a little warmer. If that doesn't work you need a refrigerant unit with an active defrost system (such as hot gas defrost) or a desiccant dehumidifier for these conditions.

Possible Answer One: The dehumidifier ices up because the room is too cold.

More usually the question is asked when a dehumidifier ices up when for months or years it has been working fine and the room is no colder than it ever was before. There are several possible explanations.

A dehumidifier ices up if the air-flow through the unit is insufficient. The commonest cause is a clogged air filter. Air filters should be regularly cleaned; most manufacturers recommend filter cleaning every two weeks. Some filters are washable, but don't put it in the dishwasher! If your filter is not washable a soft brush or a light vacuum cleaning should do the trick. As an added precaution it may be advisable to change the filter every year or so.

Another cause of poor air flow is a failing fan motor. replacement motors are available for most current models but if you are unable to replace the part yourself this too may be an uneconomic repair.

Possible Answer Two: The dehumidifier ices up due to poor air flow through the unit

Another possible explanation is a build up of dust deposits on the evaporator coil. The flow of water from the fins is slowed and ice will accumulate and once it starts the dehumidifier ices up on a regular basis. Some manufacturers recommend cleaning the coil about once a year and configure their products to enable easy access. If you are able to access the coil for inspection it should be possible to clean it.

Great care should be taken when cleaning the coil, for your own safety and to protect the coil. Ensure that the appliance is not connected to a power source before you begin. Merely switching it off is not a guarantee against an electric shock. Clean the fins gently with a rag and soapy water, a soft brush may be gently applied but take care not to damage the delicate fins. The soap must be thoroughly rinsed from the coil. A small hose may be used but try to get as little water on the fan motor as possible.

Once you are satisfied with the cleaning the unit must be left to dry thoroughly before use. This will need at least a day in a warm place. A flow of air from a fan will assist the drying. Only when you are confident that the appliance is completely dry should it be switched back on and tested. Specialist cleaning products are available such as "AC-Safe Air Conditioning Coil Foaming Cleaner" if you want to spend a few dollars to make the task a little easier.

Possible Answer Three: The dehumidifier ice up because the evaporator coil is dirty

Most room dehumidifiers have an "auto defrost" system. This is the system that turns off the compressor until the ice has melted. This system depends on a sensor detecting the ice build-up on the coil. The sensor may be faulty or the wire connecting the sensor to the switch which causes the compressor may have become detached. Reattaching the wire may be simple on some models but if a new sensor is required, and the installation has to be done by a paid professional, it may be uneconomic to repair.

Possible Answer Four: The dehumidifier ices up because he auto defrost sensor has failed

All four of the possible answers given so far will typically result in a more or less even build-up of ice over the entire coil. If the ice forms on some parts of the coil only this most probably means there is a fault in the refrigeration system.

The most common cause is a shortage of refrigerant. Recharging the refrigerant is not a job to be undertaken by amateurs. If the loss of refrigerant is caused by a leak a replacement refrigeration unit may be required. Many units come with a five year warranty on the sealed refrigeration system but this is usually hedged with conditions. The customer may be liable for shipping and other charges which may make replacement a better option than repair.

Of course, if the compressor has failed completely no dehumidifier ices up, the coil simply does not get cold. Before discarding the unit however, check that it is not a simple electrical fault such as the on/off switch not working, or the humidistat failing to switch on the compressor. These and similar faults may be relatively simple to repair.

Possible Answer Five: The dehumidifier ices up because of a fault or failure in the refrigeration system

We hope that everything has been covered by this article but, if not, please let us know how we can improve it.

What Other Visitors Have Said About This Page

Submitted Tue Aug 16 2011
By: Anon

The article was clear and concise. Thanks

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