What Causes an Air Conditioner’s Filter-Drier to Clog and How Can You Fix It?

Most homeowners are familiar with the air filter in their central air systems. It traps contaminants in order to stop them from circulating around the air in your home. However, your air conditioning system has another type of filter, too—the filter-drier.

The filter-drier is located in the refrigerant line, and its purpose is to trap contaminants in the air conditioner's refrigerant before they have a chance to harm the system. The filter-drier contains a desiccant that absorbs any water in the refrigerant, and it has a mesh screen that catches other contaminants such as dust, metal, and oil.

Unlike your air filter, it may not be easy to replace the filter-drier on your own. When your air conditioner is operating normally, it's rare for the filter-drier to need replacement. They're designed to last for a very long time. However, there's still a chance that a clog can form in the filter-drier that restricts the flow of refrigerant throughout your air conditioning system. To learn about why this happens and how you can fix the problem, read on.

What Causes a Filter-Drier to Clog?

One reason filter-driers can clog is due to age. As the desiccant inside the filter-drier absorbs water, it will become saturated and swell. If it swells too large, then it will begin to constrict the flow of the refrigerant running through the filter-drier.

A filter-drier can also become clogged if its mesh screen is full of contaminants. The refrigerant circuit in an air conditioning system should be completely closed, so no contaminants should be able to enter. If there's a hole somewhere in the refrigerant lines or in the coils, then dust may be able to enter into the refrigerant line and clog the drier-filter. In addition to dust entering into the line, oil leaking from the compressor can sometimes enter into the refrigerant line as well and cause a clog in the filter-drier.

How Can You Tell if the Filter-Drier Is Clogged?

A clogged filter-drier will show the same signs as your air conditioner having a low refrigerant level, such as a frozen evaporator coil. The refrigerant passes through the clogged filter-drier very slowly, which causes its pressure to drop as it heads towards the evaporator coil in your indoor air handling unit. The refrigerant becomes colder as it loses pressure, and the sharp temperature drop can cause your evaporator coil to freeze over. If the filter-drier is completely clogged and is obstructing the flow of refrigerant entirely, then your air conditioner won't work at all.

One way you can test for a clogged filter-drier is to check the temperature of the refrigerant lines on both sides of it. Air conditioning repair technicians use a clamp thermometer for this purpose. Since the pressure on the side leading to your evaporator coil is low, it should be noticeably colder than the side where liquid refrigerant enters the filter-drier. If the filter-drier wasn't obstructing the flow of refrigerant, the pressure and temperature of both sides would be nearly the same.

How Do You Fix a Clogged Filter-Drier?

A clogged filter-drier needs to be replaced. They're inexpensive, and it's an easy job for a professional air conditioning repair service. However, it's more important to find out why the filter-drier clogged in the first place—they're designed to last an extremely long time. Your entire refrigerant circuit, including the evaporator coil and the condenser coil, need to be carefully checked to find out how contaminants are entering your refrigerant line. Any holes in the circuit need to be patched and lose connections need to be tightened in order to prevent the replacement filter-drier from being clogged.

If you think that your air conditioning unit may have a clogged filter-drier, call an air conditioning repair service for a full system inspection. It's rare for them to clog, so make sure your system is inspected.