What Causes an Air Conditioner to Freeze Up?


If your AC unit is freezing up in the middle of summer in Elk Grove, CA, something is wrong. The reasons why this is happening are often related to a lack of consistent maintenance. This is actually good news because a system that freezes up while in use is preventable. When you notice this symptom, our team at Huft Heating and Air Conditioning will gladly take a look. Then, we can determine if any other damage has been caused. Here are the reasons why your AC unit may be freezing up.

Dirty Air Filter

The air filter is an AC unit’s front line of defense against dust, particles, and other allergens in the air. It needs to be replaced at least once a year. If your unit consists of a HEPA filter, it needs to be replaced on a monthly basis. A filter that can capture smaller particles is a filter that is extremely effective. So, if it builds up a layer of dust, the filter is going to begin restricting airflow. A system that no longer has unobstructed airflow will either begin to freeze or overheat. If the airflow is a culprit and the unit is freezing, it means that there is a combination of things happening. Often, when airflow is restricted, the equipment will overheat and stop working. If it is freezing up instead, there could be leaks, or the refrigerant level is too low.

Blocked or Closed Vents

Older homes often have ductwork. This means that the output travels from the unit to its destination through the ducts. In order for the output to actually enter the rooms, the vents have to be open. If too many vents are closed, the output has nowhere to go except back to the unit, which could be causing the freezing. If too many of the vents are blocked, it has the same effect. You may, therefore, be a prime candidate for a duct cleaning service.

Thermostat Is Set Too Low

There are individuals who want to feel like they are in the Arctic during the summer months, which is understandable. The point of having a cooling unit is to help you to feel comfortable indoors when it is warm outside. You can overdo it, however. When you lower the thermostat past its recommended settings, it has to work harder. This is not a big deal for a newer unit, nor is it too bad for a system that only has some miles on it. It is a big deal for an older unit, though. When the appliance has to cool at a lower temperature, it has to work harder. This is when you will hear the compressor click on. When the compressor clicks off, it means that the fans are working to spread out the output.

An older unit that has to work harder than it is able to may freeze up. Remember, sometimes it is a combination of factors working together at the same time. For example, if the air filter is dirty and the unit is older, plus you are asking it to produce very cold air, you are making the unit complete a task that it can no longer handle. On top of it all, the airflow is already restricted due to the dirty air filter.

It Is Already Cold Outside

Again, if you want to feel like you are in the Arctic because it helps you to sleep at night, it is understandable. You simply need to know the risks it poses for your unit. If you are running your system at a cold temperature and it is cold outside, too, you are running the risk that the appliance is going to freeze up. A cooling system takes in warm air and conditions it. Through the evaporator coils and the refrigerant, the warm air is cooled off. If it is taking in cold air, the process is disrupted. Plus, cold air usually has moisture in it. If the unit is taking in moisture, the moisture remains in the system and has nowhere to go. There is also nothing helping it to dry up.

Dirty Evaporator Coil

The most important component of an AC unit is the compressor. The compressor is considered the heart of the cooling system by industry professionals. There are several other important components, too. If the compressor is not working, cold air will not be produced. The only thing that will happen when you turn it on is that the fans will spin. When the evaporator coil is dirty, it becomes insulated. Insulation is good in several situations, except when it comes to the evaporator coil. You want your attic or basement to be insulated so that your comfortable air does not escape. When the coil is insulated, it has no way to dry up. The refrigerant running through it freezes up, and heat is not allowed to do its job.

Low Refrigerant Level

The refrigerant is the liquid that is used to cool off the warm air your AC unit takes into its system. The refrigerant goes from liquid to gas, and then back to liquid. It needs to be able to complete its process to do its job effectively. When there is not enough refrigerant, the refrigerant itself is not impacted, but the evaporator coil will be. This is why it is important for the refrigerant level to always be topped off.

Bad Blower Fan

A heating, cooling, and ventilation system is a piece of technology. It may not be the same technology as your computer or smartphone, but it is a system of components that work together to produce an outcome. Your car is similar to a cooling unit. Both use refrigerant and have other similar parts and processes. When one component is not operating at an optimal level, the rest of the parts have to pick up the slack. This means that they are compensating and working harder than intended. A bad blower fan could be the culprit of an AC unit that is freezing up. It boils down to bad airflow again. If your system is successfully producing its output, but the output is not exiting the unit due to an obstruction, the output has nowhere to go. When enough cold air remains in the unit, the result is freezing.

All of these potential culprits are why regular maintenance is important. When professionals like ourselves are given the opportunity to inspect the unit at least once a year, we can clean it up and test it. If we notice that a part is failing, we can make adjustments to get it back in shape. If it is beyond repair, we can recommend a replacement before it causes strain on the rest of the system.

To schedule an inspection for your AC unit that is freezing up, give us a call at Huft Heating and Air Conditioning in Elk Grove today. We also offer whole-house fan installation, water heater repair, and insulation services.