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What Causes an Air Conditioning Freeze Up?

A/C Freeze Ups Happen–Here’s What To Expect

air conditioner cathedral city
Air conditioner freezing up is quite a common issue these days. Figuring out the major cause can really be problematic. There are a number of reasons of freeze up and it doesn’t matter whether the unit is split or window. When an air conditioner freezes up, it’s not capable of cooling properly and also can ruin the entire internal system so you need to fix it immediately. Read here how your air conditioner freezes up:

Joule Thomson Effect

The scientific explanation: the Joule Thomson effect is a principle in thermodynamics stating that if everything is kept constant, the gas expands and the pressure decreases as temperature decreases. In the same way, as gas is compressed, the temperature will increase. The amount of energy of molecule decides the temperature and when air molecules bounce around rapidly, the air feels hot. On the other hand, if the molecules move around slowly then the air feels cold.

This is the basic mechanism of air conditioning as the system works by allowing the evaporator coil to expand the refrigerant inside. However, the coil cools rapidly and as it comes into contact with home’s air, the refrigerant absorbs the heat from the air inside the home. Next, the newly heated refrigerant transports outside of your home where it is compressed. It further causes it to heat up and transfer the heat from the inside to the outside air. This cycle keeps on repeating again and again making the inside completely cool.

Now the air conditioner freezes up because the evaporator coil is cooling more than it should. It might be because something has altered your system in a bad way. Let us see why the air conditioner freezes up.

Why Air Conditioners Freeze Up

Now that you know what can cause the air conditioning unit to freeze up, you can easily figure it out. It may happen that something is causing the Freon to expand more than it is designed to which further makes the coils colder than normal. Also, it may be because something is preventing the air in your house from transferring its heat into your system. Here are the major causes.

Insufficient air flow

The split air conditioning unit is designed to drop the house temperature by extracting heat from it and if the unit is unable to blow the inside air properly over the evaporator coil, then chances are likely that this heat exchange cannot take place and the Freon is not removing heat from the home. The temperature drops continuously and the air conditioner freezes up.

Low on refrigerant

If the air conditioner is low on refrigerant then also the unit can freeze up. Inside the system, when the pressure is low, this thing happens. It is because there is less Freon in the system but it has to expand the same amount forcibly. The more the expansion, it is equal to cooler temperature. When the evaporator coil drops below freezing, it causes the moisture in your air to freeze as it comes into contact with the coil which in turn makes it ice up.

Specific temperature range

As you may know, air conditioner is designed to function in a specific temperature range. If the air conditioning unit runs when the outside air is below 62 degrees, then it causes a freeze up as the pressure inside the system will drop.

Mechanical failure

The mechanical failure i.e. if there is a problem in the refrigerant lines or the blower fan is not working properly or there is a clogged filter dryer, it can cause the air conditioner to freeze up.
All these are the issues which cause the air conditioning freezing and it is important to know how to troubleshoot it.

How to Troubleshoot or Fix the Issue?

Just because your air conditioner freezes up, you should not think of selling the unit as it is possible to fix it. It can be the simplest thing if done in a right way but can cause problems even if a little mistake is done. So follow the steps to rule it out:

Check the filter

Check if the filter of your AC is freezing up as it is one of the most common issues found. Use a high quality filter and replace it often to avoid clogging. It is because if the air filter gets clogged then the restricted air flow causes the system’s temperature to drop below the level. However, the unit freezes up.

Check the evaporator coil

Lack of airflow can be a cause of freezing up and it can happen due to the dirty evaporator coil. It drops the temperature and cause the air conditioner to freeze up. So to make the unit keep running, clean the evaporator coil.

Air flow restriction

Next, you need to open all the air conditioning vents as any type of air restriction makes the unit freeze over. Make sure to check the vents for any leaks, clogging, bends or disconnected portions and also inspect the ductwork properly. Go to the attic and track everything carefully to avoid this issue.


If you have performed these steps and still cannot find a solution, it’s the time to see a contractor. You can also buy a new air conditioning unit if nothing works at all. As you know, freezing up of the AC unit is not a rare thing and many of us often ask this question. You might have got to know clearly the major issues that cause freezing up. Now by following these steps, you can either prevent or troubleshoot them. Ice can expand and damage the system so if you will not fix it, your system might face a big problem. Get a healthy air conditioner unit with the above steps and let it serve you for many years to come.

A HVAC contractor can help you in many ways but check the facts first before spending money for repairs.

Posted on by Desert Air Conditioning Inc
What Causes an Air Conditioning Freeze Up?

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