Troubleshooting An Icy Air Conditioning Evaporator

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Troubleshooting An Icy Air Conditioning Evaporator

Troubleshooting An Icy Air Conditioning Evaporator

19 April 2016
 Categories:
, Articles


If you have an air conditioner that suddenly stops blowing cool air through your vents, then you obviously have a problem with the device. If the evaporator unit in your basement has ice on it, then you may be able to troubleshoot the problem by yourself. If you are handy, then keep reading to find out what you should do and when you should contact a professional.

Check The Filter First

Almost all air conditioners have filters that help to remove debris and contaminants from the air before it is released into your home. If you have an evaporator unit in your basement, then you have an up-flow device where air flows upwards into the ductwork and out the vents. These systems typically have a device called an air supply plenum. This is a metal box at the base of the air distribution system where cool air initially enters the ductwork. The filter for your air conditioner is typically located at the base of the plenum. If you have never changed your air filter or if you allow your HVAC professional to do it for you during maintenance calls, then look for the filter and check it at this time. Ice will sometimes build on an AC evaporator unit simply because air flow through the plenum has been blocked, and the filter is the likely culprit.

If your AC filter looks dirty, then replace it with a new one. Do not make the mistake of purchasing a HEPA filter for the system though. While this type of filter will catch pollen and other allergens, the holes in the filter are too small. This will block airflow and you may continue to experience a cooling problem. Purchase a pleated disposable filter for the unit and make sure to check it about once a month. The filters can last three to six months, but you will want to make sure you replace it as soon as it appears dirty. 

Inspect For Signs Of Low Refrigerant 

If you change the AC filter and you still notice the ice building, then it is possible that the blower is not working. Turn on the air conditioner and listen for the sounds of the blower as the unit starts up. If you hear the telltale signs of the blower motor working, then you will need to determine whether or not the unit has enough refrigerant. If refrigerant is low, ice will build around the evaporator, even though this seems counterintuitive. 

This happens because the refrigerant running through the cooling coils does not pressurize properly. Under normal circumstances, the coolant is condensed and pressurized until it turns into a gas. This gas pulls heat out of the air inside the evaporator unit. The blower then moves the air into the ducts. However, when there is not enough coolant to fill the coils, this leads to a drop in pressure. The refrigerant will then stay in liquid form as it passes through the metal tubes. The small amount of liquid becomes extremely cold and freezes the condensation that builds on the exterior of the coils. The coolant keeps freezing the moisture until a solid layer of ice forms. 

The ice is a telltale sign that refrigerant is low. Higher electric bills, bubbling sounds around the outdoor AC unit, and a warm home when the unit is running are all signs of low coolant too. An HVAC professional from a company like Cape Fear Air Conditioning & Heating Co., Inc. will need to refill coolant and inspect the system for a leak. While you may not be able to add the refrigerant yourself, you can inform your air conditioning technician of the troubleshooting tasks you have already completed. This will help to ensure a quick diagnosis of the coolant leak and lead to a more timely and effective repair. 

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