There are a number of different defects that can cause the larger of the two refrigerant lines, called the “liquid line” or “suction line," to ice over like in the photo above. Here’s three of the most common causes:

1. Low refrigerant gas level due to leak.
2. Anything that restricts air flow, such as a dirty air filter, dirty evaporator coils (the piping on the inside unit), blocked ducts, or closed dampers.
3. Any restriction in the refrigerant flow, such as a kink in the line or restricted filter-drier.

An air conditioning technician can evaluate the problem and make the necessary repair. Low refrigerant gas level due to slow leak is the most common defect that we find causing an iced-over liquid line, but any of the other ones listed are also likely culprits.  

    Also, see our blog post Why is my air conditioner not cooling enough? and Frequently Asked Questions (FAQ) about Air Conditioning Troubleshooting.

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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 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.