It is called a "filter drier” and does exactly what the name says: it filters out small particles and removes moisture with a desiccant from the pressure line (the smaller tubing with no insulation, also called the liquid line). A filter drier is not usually installed with a brand new system, but typically added to the line after replacement of the condenser or if a refrigerant leak has made recharging the gas necessary. Any small contaminants can damage the compressor, and water in the line will generate organic acids that form a sludge-like goo that will eventually clog the expansion device at the evaporator coil. 

    Although a filter drier canister on the pressure line can be installed as preventative measure, it is considered an indicator that there has likely been some sort of previous repair to the system. Also, the filter drier itself can cause a problems when it becomes clogged and needs to be replaced.

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I find out the age of my air conditioner or furnace?

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning?

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

    Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.