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AC and Heating Tip from AC Express

What to Do When Your AC Freezes

What to Do When Your AC Freezes

It seems so counterintuitive but it’s true, the hotter the weather, the more likely that you might find ice in your air conditioner. A frozen air conditioner is no laughing matter. It’s a serious symptom that signals something that may need substantial repair. Or it could be something that’s easily fixable on your own. The problem is that there are a lot of different potential causes of a frozen AC and all of these different causes have different appropriate fixes and things you can and should do to help the situation before you call a professional.

This tip is all about helping you navigate and get through a specific air conditioning related issue that is common and often requires very specific actions in order to resolve. We’ll be going over the science behind why an air conditioner can freeze itself with no external coldness, what the most common causes of a frozen AC are, and how these different causes should be dealt with. If you rely on air conditioning in Austin and you’ve ever find yourself plagued by a frozen air conditioner and it causes you to run out of that cool air you find necessary to live a comfortable life, don’t fret any longer. Read on to learn all about this condition and what to do about it.

The Joules-Thomson Effect

Before going into the specific causes of a frozen AC unit we’re going to quickly go over some of the physics that explains why such a thing is possible from a scientific perspective. This will be a brief look and won’t go too technical or too in depth. It’s simply beneficial to understand the how before one investigates the why.

The Joule-Thomson Effect is a principle in thermodynamics that states that if everything else is kept constant, then as a gas expands, its pressure decreases, and its temperature will also decrease. As such, as a gas is compressed, its temperature will increase. This is because what we call the sensation of temperature is really just a measure of how much energy something has. If the molecules have less room to bounce around in then they are going to bounce more rapidly, thus the energy increases, thus the temperature. The evaporator coil works by allowing the refrigerant to expand rapidly. This means a decrease in pressure which causes a rapid decrease in temperature. The coil comes into contact with the air from your house as it flows over it and the now cold coil absorbs the heat from the air, cooling the air before it’s sent back into your house.

This effect, the Joules-Thomson effect, is used to allow your air conditioner to cool the air inside of your house. But any time you change part of the equation, you might throw the system out of whack. So in summary, your air conditioner is freezing up because something has altered your system in such a way that it is cooling your evaporator coil more than it should, causing the unit to freeze up. This is the “how” of an AC freezing up, this effect of temperature change due to pressure change. In the next section we’ll apply this “how” to the potential “whys”.

Determining the Cause of the Freezing

The next step is the most important one, determining the root cause of the freezing. Now that you have a basic idea of how your air conditioner uses expansion and compression to heat and cool its refrigerant, you can figure out why your central air conditioner is icing up. Your air conditioner can freeze up for a number of reasons, so we will discuss them from the most common to some of the more uncommon causes of freezing. All of these causes are rooted in the Joule-Thomson Effect discussed above, which means, simply put, your air conditioner is freezing up because something is either causing the refrigerant in your system to expand more than it is designed to, which in turn is making your coils colder than normal, or that something is preventing the air in your house from transferring its heat into your air conditioning system. Regardless, this causes your evaporator coil to drop below freezing and your air conditioner to freeze up.

Refrigerant Leak: This is one of the causes of AC freezing that can be the hardest to diagnose on your own. That’s because refrigerant leaks themselves can be hard to find. If you go through the rest of this list and you can’t find any obvious cause of the freezing around your evaporator coils, then the cause may be a refrigerant leak and you’ll need to call a professional to deal with it. The professional with have to first find the leak, then fix it, then replace the missing refrigerant.

The way a refrigerant leak causes freezing is by reducing the pressure in the system. Less refrigerant means more room for the remaining refrigerant to expand, this means reduced pressure. And according to the Joule Thomson effect, reduced pressure means reduced temperature. This can sometimes be enough to cause freezing. If someone comes by and repairs the leak and replaces your refrigerant but it happens again, it might be due to a refrigerant line that’s become too old and develops cracks frequently. You may need to replace your air conditioner at this point as the repairs will no longer be worth it based on the age and performance of your machine.

Blocked Air Flow: A lack of proper air flow over the evaporator coils can also cause the coils to freeze up. That’s because a lack of air flow means that the coils aren’t able to absorb as much heat from the air that is hotter than the cooled down coils. This means they get colder than they should and eventually can freeze up. If your air conditioner, for whatever reason, isn’t blowing enough air over the evaporator coil then the refrigerant inside isn’t able to absorb the heat of that air and therefore isn’t able to raise its own temperature. This means over time the refrigerant will continue to cool more than it should which will eventually cause freezing.

These are two of the most common causes of freezing in your AC unit, lack of refrigerant and lack of airflow. There are other causes too. One of those causes is a setting that’s too cold. Your air conditioner is designed to operate during a specific set of conditions. If you have your AC running but the outdoor temperature is around 62 degrees or lower then this can cause your coils to freeze up. The lack of heat outside will cause the pressure in the system to drop too low and cause freezing. A number of mechanical failures can also cause a drop in pressure within the refrigerant line which leads to freezing. The air blower dryer can malfunction or maybe the compressor stopped blowing. Maybe there’s a kink in the refrigerant line or a condensate drain that’s become clogged. All of these malfunctions can eventually lead to a drop in pressure, which means a drop in temperature, which can cause freezing.

Fixing a Frozen AC

Now that you know what some of the causes of a frozen AC are, you need to know what the fixes for those causes are. Knowing is half the battle, but that’s only half the battle after all. The next step is action. For a blocked airflow problem, the first step is to find the cause of the blocked airflow. A likely culprit is dirty air filters. Air filters should be changed every few months because if they’re not then the air in your home won’t be able to flow as effectively through them which can cause restricted airflow. If your air filters are dirty then change them out and you might be halfway to solving the issue.

To deal with the ice itself, first turn off the air conditioner. Keep the setting off the “cool” setting but turn the fans on. This will help the evaporator coil defrost. Give it about an hour and a half to defrost, perhaps more or less depending on how hot the ambient temperature is. Once the coils have defrosted then you can turn your air conditioner back on.

In the case of a refrigerant leak you’ll have to call a professional. They will be able to diagnose and find the source of the leak, fix it, and replace the refrigerant in your system. As mentioned in the section above, if the repair is made but the same thing happens again down the line, this might indicate that your air conditioner has gotten too old and a replacement may be in order.

Sometimes it’s not your air filters that are dirty but your evaporator coil itself. This can cause freezing because a dirty evaporator coils isn’t going to be as conductive and isn’t going to be able to take in the heat from the air as effectively. You can either clean the coils yourself in this case or you can call a professional to confirm that this is the source of the issue and clean them. Remember to turn your air conditioner off before looking inside your indoor unit and touching anything. Let the evaporator coils defrost before attempting to clean them.

Make sure there’s not anything else that could be restricting airflow. Be sure that all the vents in the house are open and that there’s nothing like drapes blocking them. Make sure that you also inspect your ductwork for leaks, bends or disconnected portions. To do this, you will likely have to go into your attic. Be careful though. If you’ve never walked in your attic before, then ask a friend who knows how to and make sure you only walk on the joists.

Air Conditioning Repair in Austin

So know you know a little more about the problem of AC freezing. We’ve gone over some of the basic science of how the HVAC system works and how it shouldn’t work. You know about the root cause of coil freezing, drops in pressure causing drops in temperature. We’ve gone over some of the most common causes of icing up and what to do about them.

If you’ve got a problem with a frozen air conditioner unit and you’re unable to take care of the issue on your own then calling a professional is in order. You need an experienced Austin AC repair professional service like the kind you get with AC Express to fix something like a refrigerant leak. AC repair in Austin is the business of AC Express, serving the Austin area from Georgetown and Manor to Lago Vista and Taylor for many years. To improve, repair, or replace your Austin air conditioning, call AC Express today!


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