What Causes an Air Conditioner to Freeze Up?

Ice-cold, freezing air conditioning is usually a good thing, especially during the hot summer months. However, when an air conditioner freezes up, that’s a bad thing. Air conditioners work through a system of controlling temperature, airflow, and pressure. When there’s an issue with any of those components, the refrigeration system in an air conditioner, which creates the cool air, can actually freeze itself. A frozen air conditioner won’t blow cool air, and may not blow any air at all.

What Causes an Air Conditioner to Freeze Up?

To understand how this can happen, it’s important to understand how air conditioning works in the first place.

An air conditioner contains a coil of cold refrigerant, which needs warm air to blow across it in order to produce cold air. The warm air also serves to keep the coils from freezing over. For instance, with an outdoor, straight cooling system, warm air from the inside is removed by an indoor coil, and transferred to an outdoor coil, where it is pushed out. If you’ve ever felt the air blowing out of an air conditioning unit outside, it probably felt warmer than the outside temperature. That’s because the system is pulling the air from the inside, and discharging the extra heat outside.

The coils in an air conditioner use pressure to manipulate the airflow, which keeps the air blowing over the refrigerant coils. If the warm air stops blowing over the coils, or if the pressure is off in any way, the coils can become too cold, and become frozen. There are a few reasons for this. Let’s take a look.

First, it’s worth mentioning that high humidity can make the freezing issue worse. That’s because the more moisture that comes in contact with the accumulating ice, the more ice builds up on the coils. The ice can actually start moving up the copper pipes of the unit, all the way to the compressor.

Now, let’s take a look at some of the reasons a unit freezes up in the first place.

1. Insufficient Air Flow

This is the most common reason an air conditioner freezes up. This can be caused by a range of issues, from malfunctions in the blower motor to problems with the air intake. Whatever the exact issue is, as soon as warm air stops flowing over the coils, freezing and ice-accumulation can start.

2. Blocked Air Duct

Air moves through ducts in your home, so it goes without saying that any issue with an air duct, such as a collapse or blockage, can wreak havoc on your air conditioning system. Even if everything else in the system is running well, a reduction or issue with air flow can lead to freezing of the unit.

3. Failed Blower Motor

The blower motor does just what it sounds like: It blows warm air over the coils. If it breaks, or there’s an issue with it, the air flow over the coils could be disrupted, leading to ice buildup. A failing blower motor may sound inconsistent while it works, or may even rattle.

4. Low Voltage in the Home

In case you haven’t noticed, your electric bill usually goes up over the summer, when your air conditioner is being used more. This is because the unit runs on a number of high-power components to keep your home cool. If there isn’t enough voltage coming through, it could impact either the blower motor or the fan, leading to a lack of air flow over the coils. This, of course, can lead to the coils freezing up.

5. Dirty Air Filters

It’s easy to forget that there’s a filter blocking the dusty air in your home from entering the air conditioner, keeping the air and the unit clean. If you have forgotten about this, it’s quite possible the filter is clogged. A clogged filter restricts air flowing into the unit, and can lead to the unit freezing up.

6. Dusty Coils

If you happen to run your unit without a filter, a low-quality filter, or a dirty filter, it’s possible that dust can accumulate on the coils. The accumulated dust can act as an insulator on the coil, preventing the warm air from reaching it. This can lead to freezing.

7.  Refrigerant

Lack of refrigerant in the system can cause big issues. Essentially, the compressor in your air conditioner compresses refrigerant after the heat from inside is released. The war air converts the refrigerant into a gas. The refrigerant heats up, and drops the pressure in the system. It’s then converted back to a liquid, and pumped toward the blower motor in the house.

If there isn’t enough refrigerant, compressing the refrigerant to a gas happens too early in the process, creating enough cold to bring moisture on to the coils. The moisture instantly freezes on the coils, and ice can accumulate, the longer this process continues. It’s vitally important to maintain proper refrigerant levels in your air conditioning unit.

What to do if I find this problem

If your air conditioner is blowing warm air, and appears to be frozen, the first step is to turn the thermostat off, while leaving the fan on. This will allow the coils to thaw out, as the airflow will continue through the system, without it being tasked to make the air cool. Checking and changing the filter is also a good thing to do, especially if it’s full.

Calling a repairman should be your next step, as they’ll be able to diagnose what, exactly, went wrong, and fix the problem. Make sure to let the repairman know what you’ve done, in terms of keeping the fan running and checking the filter. This will help them in diagnosing the problem. Despite the headache, a frozen air conditioner can be fixed, and you should be back in cool, well-regulated comfort before you know it.