Why Is My Air Conditioner’s Refrigerant Line Covered in Ice?

This is an evaporator coil (on left).

DO THIS RIGHT NOW: Turn off your AC and turn the fan setting to “On.” This will unfreeze the evaporator coil and prevent any damage to the compressor (a very expensive part you don’t want to replace).

Now, let’s delve into what can cause an evaporator coil to freeze up and what you can do to ensure this never happens again.

What causes the evaporator coil to freeze up?

An evaporator coil, a group of copper tubes, freezes when the refrigerant flowing through the tubes gets too cold, causing the moisture in the surrounding air to freeze.

So what causes the refrigerant to get too cold? Usually, it’s one of two things:

• Low airflow over the evaporator coil
• Low amounts of refrigerant

What can cause these two problems?

Let’s divide the possible causes into things you can solve right away and things you’ll need a technician to solve.

Problems you can fix:

Clogged/dirty air filter—A dirty filter reduces airflow over the evaporator coil, causing it to freeze. Check the filter at least once a month.

Closed supply vents—Don’t close supply vents (the vents that blow air out)—even in unused rooms. Closing vents reduces airflow over the evaporator coil.

Blocked return vents—Ensure that furniture or curtains aren’t blocking the return vents (the grates where air gets sucked in).  Like closing supply vents, this reduces airflow over the evaporator coil.

Problems a technician needs to fix:

Refrigerant leak— The main cause of low refrigerant is a refrigerant leak. The technician needs to evacuate the remaining refrigerant, and then find and—if possible—fix the leak.

Malfunctioning indoor blower—  If the blower isn’t working properly, there may not be enough air blowing over the evaporator coil, causing it to freeze up.

Dirty evaporator coil— Dirt blocks airflow over the evaporator coil, causing it to freeze up.

Note: This list isn’t exhaustive; it’s just a quick overview of common problems.

Summary: What now?

Change the filter, and open and unblock any supply and return vents. If your evaporator coil (and refrigerant line) starts to freeze up again after doing these tasks, then you need a technician’s help.