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What causes an air conditioner to freeze up?

As part of our air conditioning checkup here in Albuquerque, we'll check your AC unit's refrigerant levels.

Picture this: it’s the hottest day of summer. The sun is beating down on your home. You feel the temperature inside start to rise, but you no longer hear the distinctive sound of your air conditioner at work. After fiddling with the thermostat, you walk outside to a strange sight: despite the hot weather, your air conditioner condenser is iced over. Appropriately, this is known as an air conditioner freezing up, and it’ll leave your home without cooling if not fixed.

So, what causes an air conditioner to ice up? In actuality, there are several different things that could be happening that might cause this issue. In this article, we’ll review the most likely scenarios and review your next steps for defrosting your AC and getting it running again.

Why do air conditioners ice up?

We get plenty of calls from homeowners in Albuquerque asking us the same thing: “Why is my air conditioner freezing up?” While there are some common issues that lead to this phenomenon, it’s not always possible to diagnose the issue over the phone. You’ll need to have one of our AC repair technicians out to take a closer look and help defrost the system.

Here are some potential reasons your air conditioner has iced up:

Common: Low Airflow

First, let’s start by reviewing how air conditioners work. At their most basic level, all AC units do is move heat energy from one place (inside your home) to another (outside your home). They use refrigerant to accomplish this.

Think of the indoor evaporator coil and outdoor condenser coil as separate train stations, with refrigerant serving as the train that runs between them. At the indoor station, the refrigerant absorbs heat energy. It then carries this energy to the outdoor station, where it is released into the air, cooling the refrigerant. This refrigerant is then cycled back inside to repeat the process, again and again, until your home’s indoor temperature cools.

However, there’s an important factor to this process: to properly absorb heat energy from inside and take it outside, the evaporator coil needs a consistent airflow. If the coil does not absorb enough heat energy indoors, it will start a runaway cooling process, with the refrigerant becoming more chilled as it cycles. Ultimately, the refrigerant becomes cold enough to “ice up” the outdoor condenser. If there’s enough humidity in the air, you’ll see this as actual frost or ice on the unit.

In a vast majority of cases, an AC unit keeps freezing because of insufficient airflow. This could be due to a clogged air filter, a malfunctioning blower unit, or a larger issue with your air ducts that is preventing indoor air from traveling from the air intake to the evaporator coil.

Less Common: Low Refrigerant

Pressure plays a key role in the refrigeration cycle. If the refrigerant line loses pressure, it is unable to absorb or transport heat energy as efficiently, which could lead to icing issues.

However, this is typically a less common reason why an air conditioner keeps freezing up. For one, the refrigerant used to transport heat energy is supposed to exist in a closed-loop system. Under ideal circumstances, it does not leave its pipe: unlike a car, your home’s air conditioner is capable of using the same refrigerant, year-after-year, and shouldn’t need periodic “recharging.” For a refrigerant line to lose pressure and refrigerant, something has gone wrong with the line. There is likely a leak.

Your next steps

If your AC has frozen over, you need to call your local HVAC experts at Wagner. Our technicians are specialists when it comes to diagnosing air conditioning issues. We’ll run through our checklist and work to determine the root cause of the issue. As detailed in this article, the answer to “what causes an air conditioner to freeze up” is typically something minor, such as insufficient airflow. However, we’ll also want to rule out more serious issues, such as refrigerant loss or a problematic blower.

Never try to defrost your own air conditioner. Attempting to chip away at ice can lead to damage to the system. Go to your thermostat and turn off the cooling setting: you don’t want your air conditioner to continue the cycle that is causing it to freeze up. Instead, just turn the fan on—maximizing airflow will help with the defrost process and reduce the amount of time it takes our technicians to get your air conditioner back to normal.