Why Do Air Conditioners Freeze Up? 

In midsummer when there’s a high of 90℉ every day for as long as the forecast can predict, an icy wonderland might be something that you dream about. But when the icy wonderland is on your air conditioner, it won’t make you any cooler or any happier. Air conditioners can freeze up under lots of different circumstances. Each of them means that your air conditioner needs some help to start cooling down your home again. Hopefully, we can shed some light on why you have a frozen AC and what to do about it. 

How Does Your AC Work? 

You’ll need some basic information about how your air conditioner works before you’ll be able to make sense of why it’s covered in ice. Here’s a quick physics lesson to get you started: When two things are touching and one is warmer than the other, the heat from the warmer object is always transferred to the colder object until both are at the same temperature. Air conditioners take advantage of this rule by using refrigerant, a substance that is, by nature, colder than other substances. 

The refrigerant lives inside tubing that runs in a circuit from the inside of your house to the outside. When your thermostat tells your AC that it’s too warm inside, the process of heat transfer will start. As soon as your AC turns on, a fan starts pulling warm air from your home, through the return vents, and into the air conditioner. It blows over the evaporator coil where the refrigerant inside absorbs the heat from the air, making the air cooler. The cold air is pumped back into your home. 

Meanwhile, the heated refrigerant goes outside where it enters the compressor. The compressor pressurizes it and superheats it. The refrigerant then goes to the condenser coil where outside air is blown across it. The cooler outside air absorbs the heat from the refrigerant, cooling it down. Then the refrigerant goes back inside where the cycle starts again.

Why is My AC Freezing Up? 

When something goes wrong in the heat transfer process, you can start to get problems with your air conditioner. One of those problems is a frozen AC. The root of almost all freeze-ups is a lack of airflow. If there isn’t enough warm air passing by the evaporator coil, the refrigerant will get too cold. Then, any condensation that is on the evaporator coil will freeze. 

There are many different situations that can keep air from flowing properly through your system. Here are some of the main causes:

Dirty Filter

The most common cause of frozen air conditioners is also the easiest to fix. Dirty air filters can keep air from flowing properly through the system. Even if you change your filter every 1-3 months as recommended by your manufacturer, there are still situations that can cause it to get blocked up faster. If you are stirring up a lot of dust by doing home maintenance or you have a pet that sheds, the filter can get clogged quickly. The first step in any AC freeze is to change your filter. 

Blocked Vents

You have two kinds of vents in your home, blower vents and return vents. Return vents pull the warm air into the system and blower vents blow the cold air out. If your vents are clogged or blocked, air won’t be able to get to where it needs to go. Make sure to never block vents with furniture, boxes, or anything else. 

Blower Motor Isn’t Working

When your blower motor isn’t working, it won’t be pulling warm air into the unit. This will cause things to freeze up fast. You’ll know your blower motor isn’t working if it is hot, there is no airflow, or your AC is making screeching noises. 

Dirty Evaporator Coil

Most evaporator coils are shaped like an upside-down V. Sometimes the underside of the coils can get dirty, keeping warm air from getting to the evaporator coils. The coils will need to be cleaned before the system will be able to run properly again. 

Low on Refrigerant

When there isn’t enough refrigerant in your AC, the pressure in the refrigerant lines will go down. As pressure goes down, so does the temperature of the remaining refrigerant. It will drop below freezing and freeze any condensation that is on the evaporator coil. You’ll need a local HVAC professional to fix your refrigerant leak and recharge your AC.

Setting Thermostat Too Low

Setting the temperature too low on your thermostat can cause your AC to freeze up. If your AC is running too much to keep up with the low temperature setting, the temperature in the coils can get too cold and cause a freeze. Make sure to set your AC no lower than 67℉.

What Should You Do About a Frozen AC? 

When you notice that there is ice building up on your air conditioner, the very first step is to turn off your air conditioner. It won’t be able to cool your home down when it’s frozen so it won’t be doing you any good. However, running your AC while frozen can damage expensive parts of your AC like the compressor. 

Once your AC is turned off, turn your thermostat to the fan setting. You’ll want to keep air flowing through the unit to help the ice melt faster. After this, you’ll have to wait. It can take up to two days to thaw off completely. While it’s thawing, watch out for water leaks. The thawing water is going to drip down onto the floor so keep a bucket and some rags handy.

Change your air filter and unblock any vents that you have covered up. If your AC freezes up again after these simple steps, then something else is the culprit. For any other problems, you will want to have a local HVAC professional come and diagnose the problem. They can check your whole system and make sure everything from your control board to your blower motor is working properly. 

Air conditioners can freeze up for many different reasons. If it has happened to you, don’t worry! Your friends at Stith Plumbing & HVAC can help. If you are in Springdale AR, or the surrounding areas, give us a call for AC troubleshooting and repair.