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Air Conditioner Icing Up Causes

Last updated on March 5, 2025 Buying Guides

While the main function of an air conditioner is to provide a cold environment, if an air-conditioning system is producing ice it can actually be detrimental to the unit. As ironic as it seems, a unit freezing over could break the entire system and can actually turn your ice-cold day into a sweltering hot, AC-free one.

If you’ve spotted icicles on the coils on the outdoor unit of your air conditioning system, then it’s likely that your aircon unit is freezing up and well on its way to seizing up. Not to mention, you’re probably feeling warm air blowing from your system.

To avoid the problem escalating further and causing a huge dent in your pocket, take a look at our checklist of what could be causing the problem.

A Dirty Air Filter

One of the most common causes of a frozen air conditioner is insufficient air flow. There are numerous ways that the air flow can be obstructed, but it frequently comes down to blocked or clogged air filters.

An aircon filter collects dust and debris and if it’s not changed in due time, it will prevent sufficient air from flowing through the evaporator coils. In this scenario, a coil will begin to develop an ice layer that will continue to grow into a thick sheet of ice until the problem is solved.

It is recommended to change your air filter every ninety days. Although replacing an air filter may sound straightforward, there are many different styles, types and sizes of air filters on the market. So, if you’re not familiar with AC units it can become confusing. Rather than damaging any expensive parts, it’s a better idea to get an air con technician to come over and quickly change the air filter for you.

Objects Restricting Air Flow

Another way that the air flow can be obstructed – resulting in a frozen AC unit – is through something as simple as furniture placement.

A tall piece of furniture, like a large wardrobe or a curtain, positioned on or over a vent will block adequate air flow and, consequently, result in your air conditioner freezing up.

If this is the case, the answer is as simple as rearranging your room to make sure the vent is obstruction-free so that it can achieve adequate air flow.

A Grimy Evaporator Coil

Air conditioner systems have a drip tray that catches condensation from the humid outside air and prevents it from dripping out of the system onto your walls. In a functional unit, the water is eventually drained down through condensation lines and out of your room.

However, when water becomes stuck in the line it will freeze over, causing a clog. When a line freezes over, the subsequent evaporator coil also freezes over which is detrimental to a unit. The frozen evaporator coils and lines can restrict air flow and cause air conditioners to struggle or not work at all.

These clogs can happen from something as simple as debris, dust, hair or grime being caught in the lines.

To avoid a dirty evaporator coil and clogged lines, it’s important to schedule -or undertake – a regular clean of the drip tray, condensation lines and evaporator coils.

Low Levels of Refrigerant

One of the common culprits for a dysfunctional AC unit is low refrigerant levels. While simply topping up the refrigerant may seem like an easy fix, as we’ve delved into in other articles, a lack of refrigerant is usually a symptom of a deeper problem in the unit.

Air conditioners operate on a closed-loop system, so they shouldn’t need topping up and low refrigerant levels often signify a leak within the AC unit.

The icy build-up happens when a unit attempts to operate with less refrigerant than intended, which causes a drop in pressure. In turn, the dip in pressure forces evaporator coil temperatures to dip below freezing. The low temperature then causes water vapor to freeze onto the surface of the coil and generates the ice.

So, if refrigerant levels are the reasons for your AC unit freezing over, it’s very important to undertake a thorough check for any leaks through the system.

Mechanical Problems

The most complex problem associated with an aircon freezing over is mechanical issues.

Some common mechanical issues include a slow or faulty fan, a problem with the electronic control board or a defective thermostat.

Malfunctioning physical parts of an air-conditioning unit can restrict airflow and cause the system to work overtime. This can cause permanent damage to both the parts and the entire system.

When there is a problem with the physical parts of your air conditioning, it’s time to call in the professionals. Changing mechanical parts can be technical and taking to your unit with tools and attempting to fix it yourself can often leave you in an even bigger mess than you began with.

FAQs

Is it okay for an AC unit to run all day?

As tempting as it may be to head out and switch your air conditioner on with the intention of coming home to a cool room, it can damage the internal parts of the unit and shorten the system’s life.

If you don’t see that as too big of an issue, then it’s generally safe to leave your AC running all day long. Air conditioning units are built under strict safety measures and should not cause a fire.

However, running an aircon all day will surely increase your electricity bills. Most modern air conditions have a timer function, so you can pre-set the unit to turn on shortly before you’re due home.

Can I pour hot water on a frozen air conditioner?

At the sight of icicles on the outdoor unit of your air conditioner, pouring hot water on them to defrost may seem like an easy fix.

To instantly melt the ice it is okay to pour hot water directly on the site, but make sure the AC is disconnected from the main power source and that the water is only poured on the evaporator coils.

However, do keep in mind that when an AC unit freezes, it is signifying that something is wrong with the system and it’s important to get to the root of the problem.

Learn more about common issues people have with air conditioners

Having trouble with your air conditioning and can’t quite figure out what the problem is? There could be a few reasons why it’s not working as well as it used to, and in our experience, these are the most common culprits:

What are most air conditioner breakdowns caused by?

Air conditioners can stop working for a variety of reasons, but most breakdowns stem from a few common issues. Whether it’s a clogged air filter, a refrigerant leak, or an electrical malfunction, these problems can reduce efficiency and even cause complete failure. Below are the most frequent reasons AC units break down.

There are many more reasons your air conditioner may not be working, and our first step with any repair job is to diagnose the issue with an initial inspection.

Get a free quote on air conditioning repairs in Brisbane

Whether your air conditioner is making odd noises, blowing warm air, or just not cooling your space properly, it might be time for a repair. We offer expert air conditioning repairs in Brisbane and can provide a free quote so you know exactly what’s needed to get things back on track.

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