How To Repair A Dehumidifier When The Coils Are Freezing Up
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- 32 repair stories
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Humidity Control
If the coils on your dehumidifier are icing up and you have verified that the ambient temperature is above 65 degrees Fahrenheit, then you may have a fault with the humidity control. Also known as the humidistat, this device works like a thermostat except that instead of the internal electrical contacts being activated by temperature, this control operates by sensing the relative humidity level. The electrical contacts supply power to the compressor circuit and sometimes the fan motor circuit. If the humidistat does not sense the correct relative humidity or if the contacts stick closed, then the compressor will continue to run and the evaporator coils may ice over. With the unit unplugged, rotate the control knob and listen for the contact set to open and close, or use a multi-meter to check for continuity. If the contacts do not go open circuit as you adjust the control, then it will need to be replaced.
Blower Wheel or Fan Blade
If the coils on your dehumidifier are icing up and you have verified that the ambient temperature is above 65 degrees Fahrenheit, then you may have a problem with air flow. For proper operation, a dehumidifier needs to have an adequate amount of air blowing across the evaporator and condenser coils to prevent frost or ice buildup. If you feel little or no air coming through the grille area and the filter is clean, then remove the cover and check the fan area. Inspect the coils to make sure that they are not restricted with lint or dirt and clean them if necessary. Inspect the blower wheel or fan blade for any signs of damage or distortion and verify that there is no evidence of any obstruction to prevent free movement. Clean the blades or fins of the blower if they have any dirt buildup, or replace the blower wheel or fan blade if any defects are found. Make sure that the fan motor rotates freely and that the fan blade or blower wheel is firmly attached to the motor shaft.
Fan Motor
If the coils on your dehumidifier are icing up and you have verified that the ambient temperature is above 65 degrees Fahrenheit, then you may have a faulty fan motor. For proper operation, a dehumidifier needs to have an adequate amount of air blowing across the evaporator and condenser coils to prevent frost or ice buildup. If you feel little or no air coming through the grille area and the filter is clean, then remove the cover and check the fan area. Inspect the coils to make sure that they are not restricted with lint or dirt and clean them if necessary. Make sure that the fan motor rotates freely and that the fan blade or blower wheel is firmly attached to the motor shaft. Using caution, operate the unit in a fan only mode and observe the fan motor. If it hums but does not rotate or only rotates slowly then it is defective and will need to be replaced. If the motor does not rotate and does not appear to make any sound, it may still be defective, but will require further testing by someone who is comfortable with using a multi-meter and working with live electrical circuits.
Bi-Metal Thermostat
If the coils on your dehumidifier are icing up and you have verified that the ambient temperature is above 65 degrees Fahrenheit, then you may have a fault with the bi-metal defrost thermostat. Some models of dehumidifiers are equipped with a defrost thermostat to de-ice the evaporator coils in conditions of high humidity or low ambient temperatures. The thermostat senses the evaporator temperature and, if it is too low, will interrupt power to the compressor but leave the fan running to blow air over the coils and melt the frost or ice. If the thermostat does not sense the evaporator temperature accurately then the compressor may run too long and create an icing condition. Testing the thermostat for continuity is difficult because it is dependent on temperature. If the evaporator coil is iced over and the bi-metal thermostat is making positive contact with the coil, then you should suspect that it is defective and needs to be replaced.
Humidity or Temperature Sensor
If the coils on your dehumidifier are icing up and you have verified that the ambient temperature is above 65 degrees Fahrenheit, then you may have a fault with the humidity sensor or temperature sensor. Many Electronic Control models use sensors to monitor the relative humidity of the room and sometimes the temperature of the evaporator coil. The control board uses that information to operate the compressor and fan motor circuits. A faulty sensor assembly may not correctly detect the relative humidity or evaporator coil temperature and cause the compressor circuit to stay energized too long, resulting in an iced over evaporator coil. Testing the sensors with a multi-meter is not usually accurate enough to give a confident diagnosis but many Electronic Control models will produce a fault code to help identify a faulty sensor assembly. Verify that the sensors are properly connected to the control board and are positioned correctly on the unit.
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