Why AC Freezing Up? -Troubleshooting Guide

You might be surprised to find a chunk of ice on your outdoor AC unit on a hot summer day, but the truth is that this can happen.

An air conditioner can freeze up due to poor airflow which, in its turn, can be caused by a clogged filter, dirty coils, and leaky ducts. Low refrigerant levels, clogged condensate drains, and issues with the blower fan can also make the coils freeze.

What exactly should you do if your AC gets covered in ice? You’ll find the step-by-step guide below.

Why AC Freezing Up?

To understand why an air conditioner is even capable of freezing up, you must first figure out how an air conditioning system works.

The evaporator coils in a cooling unit are filled with a substance called ‘refrigerant’. It has the ability to turn from liquid to gas and back again and this is exactly what allows the refrigerant to absorb and release heat. When the warm indoor air passes over the coils with the cold refrigerant, the air cools down. After that, the compressor changes the liquid substance into a high-pressure gas that is sent to the outside coil where the absorbed heat is released.

If something goes wrong in this process, the cold refrigerant can make the AC unit freeze. Here are a few things that might be to blame, in such a case:

  • Poor airflow – if there is not enough warm air flowing over the evaporator coils, they will freeze. A clogged air filter, dirty evaporator coils, and collapsed air ducts can block the airflow
  • Low refrigerant levels – the substance does not get used up during the operation process. This means that if the refrigerant levels are low, there is a leak in the system, and ice will get formed around the leak
  • A faulty blower fanif the fan is malfunctioning, there won’t be enough air flowing over the coils
  • Clogged condensate lines – not only heat but also moisture gets removed from the air traveling through the cooling system. If the drain line gets blocked, the moisture will get trapped right next to the cold evaporator coil and will eventually freeze

What Causes AC to Freeze Up in Summer?

The chances are high that if your air conditioner ever does freeze up, it will happen in the summer. That is because we do tend to use ACs the most during this season and, consequently, the majority of system breakdowns occur in this period as well.

All the factors mentioned above can make your unit freeze up in the summer, but the most common reason behind an air-con covered in ice is the lack of proper airflow. This can be caused by:

Is It Normal for the Outside AC Unit to Freeze Up?

Your outside unit might get covered in ice on a freezing winter day and that would be relatively normal. But if the AC freezes up in the summer, then it’s not okay. This means that there is something wrong with the cooling system.

Read: Does Closing AC Vents Save Electricity?

Why Does My AC Freeze Up at Night?

For the air conditioner to run effectively, the outdoor temperatures have to be within a certain range. If the temperature is way too low, the pressure inside the system can drop and this will make the unit freeze up.

Have a Question? Ask HVAC Technician

Click here to use the chatbox to speak with one of our technicians.
No in-home service calls. No appointments.

Your AC might be freezing up only at night, if it’s early summer or late spring, for example. During this time, the day temperatures might be quite high, but the nights can get very chilly.

Thankfully, the fix for this issue is relatively simple. Turn off your AC at night if you know that the outdoor temperatures are going to be low and open the windows instead.

Read: Are HVAC Service Plans Worth It?

How Do You Tell If Coils Are Frozen?

The indirect signs of frozen coils include:

  • An AC that is blowing warm air – if the coils are frozen, the air that is traveling throughout the system won’t get cooled
  • An unresponsive AC unit – if you try to decrease the temperature on your thermostat, the air conditioner will fail to adjust (the truth is that decreasing the temperature would actually freeze the coils even more)
  • A fan set to ‘on’ that is not increasing the amount of cool air – usually, making the fan work while the AC is operating will help you cool the space a bit quicker. If the coils are frozen, that will not happen, even if you switch the fan setting to ‘high’.

If you suspect that your air conditioner is frozen, the only way to confirm that is by checking the actual coils. Shut off the power to the unit, remove the access panel, and expose the coils. If you see brownish or white ice on the component, then your AC is actually frozen.

Will a Frozen AC Fix Itself?

Your air conditioner can ‘unfreeze’ itself if you turn it off completely. Increasing the temperature on the thermostat will not help, you have to make sure that the system has been shut down.

While you’re waiting for the ice to thaw, you can make sure that the air filter is clean and that nothing is restricting the airflow at the vents.

Read: How To Do Air Balancing HVAC In A House?

How Long Does It Take an AC Unit to Unfreeze?

Depending on the ice buildup, it can take your air conditioner anywhere from an hour to a full day to unfreeze.

What Happens If You Run Your AC While It’s Frozen?

You should not continue running your cooling system if you have found out that it’s frozen. In such a case, the ice buildup will increase. Moreover, continuing to run the system while it’s frozen can seriously damage your compressor.

By the way, you might not even be able to effectively cool your house if the coils are frozen, so simply turning the system off and patiently waiting for an HVAC technician to show up would be the best possible decision.

How Do You Fix a Frozen AC?

There is not much a regular homeowner can do to fix a frozen coil. The best plan would be to:

  • Turn the air conditioner off at the thermostat
  • Turn the fan setting to ‘on’ – this will force the fan to blow warm air over the coil which will help make sure that the ice thaws faster
  • Keep an eye on the drain pan – you might want to put a few towels around the indoor unit as when the ice starts melting, it may overflow the drain pan
  • Make sure that the condensate drain is not clogged

Even though the coil will fully unfreeze in about a day, it does not mean that you have fixed the problem. If the issue had nothing to do with a dirty air filter, then you should consider calling an HVAC technician.

Read: Is Closing Vents Bad For HVAC?

Can I Pour Hot Water on Frozen Air Conditioner?

Pouring warm water over a frozen coil is generally considered to be safe. In some cases, this might help thaw the ice a bit quicker. But this will not fix the root cause of the problem.

Do bear in mind that hairdryers and heaters should never be used to melt the ice on frozen evaporator coils as this can damage the unit’s electrical components.

How Do I Prevent My Air Conditioner from Freezing Up?

There are a few things that you can do to prevent your AC from freezing up.

  • Check and replace the air filter on a regular basis
  • Make sure that the supply and return vents are not blocked – the air return vent, for example, needs at least 6-12 inches of free space in front of it
  • Ensure that the condensate drain line is not clogged
  • Schedule regular HVAC check-ups

Read: How To Remove And Replace Attic Insulation That Fell Off?


Your air conditioner can freeze up due to low refrigerant levels, clogged condensate lines, and a faulty blower fan. However, the most common reason for frozen coils is the lack of proper airflow.