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What to Do When Your AC Unit Freezes Up


If one day you’re cooling off on a scorching hot day, and the air conditioner you’re using suddenly freezes up, what would you do? How can something that operates all day during the hottest days of the year be prone to freezing? 

Despite the irony of an air conditioner freezing in the middle of the summer, this does happen frequently. Unfortunately, only a few homeowners know enough about air conditioners to solve this issue without the help of an expert. 

As a result, it’s a problem that may quickly transform a pleasant summer day into a sweltering one. Let’s explore this article on the causes of this issue and know what to do when your AC unit freezes up.

What Happens When an AC Freezes Up?

If your AC freezes up on a hot day, you will notice it quickly. Potentially, serious issues appear when an air conditioner freezes and once it occurs, the only way to fix it is to allow it to thaw.

Here are signs to watch out for that will tell you whether your AC system is frozen:

Minimal Cold Air Coming Out of the Air Conditioner

There is not enough air coming out of your vents, and the temperature in your home increases. It is the most evident indicator. Its airflow is blocked by the ice in the evaporator coil, causing the supply of air movement to practically blow out of the vents.

Frost on the Refrigerant Lines

Frost on the copper cables is the most evident visual sign. As the copper leaves the AC system, the frost accumulates and becomes visible. In extreme circumstances, a solid block of ice may form on the outdoor unit, which may take some time to melt.

What Causes Inside AC Unit to Freeze?

Every air conditioner requires a constant flow of warm air to operate normally. If the warm air from your home does not reach the refrigerant, it freezes any moisture on the evaporator coils and becomes so cold.

As a result, air conditioners freeze when problems with the airflow inside the air conditioning unit or issues with the refrigerant flow occur. Let’s look at the various causes that could be causing your air conditioner to freeze:

Air Filter Blockages

Air conditioners require proper airflow to function correctly. The AC filters are one of the typical difficulties, so homeowners should start by looking there. If these become blocked air filters, there will not be enough cool air moving across the evaporator coils. Since no heat transmits to the refrigerant, the coil temperature will continue to drop. It will eventually become frozen AC coils.

Various Airflow Obstructions

Few homeowners recognize the significance of adequate airflow. They make it a habit of changing the AC filters before they become unclean. It’s a fantastic routine that they should continue. However, this may not be sufficient to prevent AC freezing. For example, clogged vents and registers prevent adequate airflow. Therefore, homeowners should check them as part of the basic troubleshooting process.

Items like furniture, curtains, indoor plants, and other things might be too close to these air routes. If so, make appropriate changes. Call HVAC experts to examine the duct system if your AC keeps freezing. The installation or design may be flawed.

Refrigerant Leaks in Air Conditioners

A frozen AC could indicate a low refrigerant level. It can occur if there are leaks in their path. Homeowners may notice a surge of heated airflow from the AC or hear a hissing sound. This issue won’t just go away by itself. The leaks need repair right away to stop any further damage.

To return to normal levels, technicians have to add more refrigerant. Due to the substance’s toxicity, homeowners shouldn’t experiment with this. A qualified HVAC technician can manage the situation safely since they can provide the right equipment.

Dirty Evaporator Coil in an AC Unit

Problematic evaporator coils are the fourth factor that causes a frozen AC unit. Owners of older systems may fail to detect the accumulation of dirt over time.

As a result, the coating of dirt and grime will act as a barrier between coils and outside air. The coils will get colder than they should be because it will hinder heat transfer. In addition, dirt can obstruct the condensate lines, trapping water that is then prone to freezing. All of these factors will increase energy usage and system workload.

Incorrect Thermostat and Fan Settings

Low fan temperature settings impact how effectively your AC unit distributes heat from the inside to the outside.

When the outside temperature is extremely high in the summer, the fan should run at a high speed to lower the inside temperature. A low fan speed strains the unit and makes it difficult to maintain the temperature.

In this case, limited air circulation paired with a cold refrigerant circulating the unit causes ice to form on the coils.

Frozen HVAC System Due to Cool Summer Nights

Usually, air conditioners are regulated to function within a specific range of ideal temperature thresholds. An AC can malfunction when summertime evenings are colder than the optimal threshold can tolerate.

Will an AC Still Work if Frozen?

Never operate the air conditioning system when there are frozen evaporator coils. Running an air conditioner with frozen coils strains the AC compressor, which is the most expensive part of your air conditioning system. Turning off the cooling system stops the passage of cold refrigerant into the frozen area.

Ensure the ice from the frozen HVAC coils subsides and dry your evaporator coil. After drying, switch the blower back on and restart the system. Only allow the fan or blower to run on the thermostat. The air circulates around and through the HVAC coils, permitting them to dry fast. Once dried down, your AC system may operate normally.

How Do I Fix an Air Conditioner That is Freezing Up?

Try these steps to see whether your air conditioner can still work even if it’s frozen:

Thaw the Frozen Air Conditioner

Turn the AC system off at the electrical breaker and use your thermostat. But first, check if the thermostat is providing power to the system. If it is, then this will stop the cooling. Turn on the fan without using the auto mode. It will blow warm air onto the coil as it circulates air around it. This will accelerate the defrosting process.

Just wait and allow enough time for the frozen refrigerant line and evaporator coil to let the ice thaw. In extreme cases, the ice is visible on the outdoor AC unit and your home’s exterior wall. As a result, this could take all day to thaw.

Make sure the refrigerant is not frozen before it reaches the compressor. The compressor’s design is specifically to receive hot vapor. It is significantly costly to change a worn-out compressor.

Inspect and Replace Your Dirty Air Filters

A small amount of dirt may cause insufficient airflow.

Get rid of your air filter if it appears dirty. Also, be sure to change your dirty air filter to a new one. You don’t want the airborne dust to gather on the evaporator coil. Your air conditioner can freeze as a result.

Examine Your Vents

Search for and remove anything that might be in their path on either side. There might be a closed supply vent in a hidden nook that you forgot about. Therefore, check every room for closed vents.

Turn On the AC Unit Again

Lastly, run the AC unit normally while you monitor it. If ice begins to develop again, switch it off but turn on the blower fan to allow the ice to melt. Then, contact an HVAC professional.

But of course, the best method to solve problems like an AC condensate drain line that has frozen solid is to avoid them from happening in the first place.

How to Prevent a Frozen Air Conditioner Unit

And now that you have discovered the causes and fixes when your air conditioner freezes up, how can it be avoided in the first place? Here are some preventive measures you may take to avoid having your HVAC system freeze up:

Replace Your AC Filter

A dirty air filter is one of the main factors for a frozen HVAC system. The air filter will allow clean air circulation in your home. It becomes clogged with dust, pollen, grime, and other irritants as time passes. It reduces airflow and causes the HVAC coils to freeze.

It is usually advisable to check your filter once a month. Adjust it as necessary. For the majority of people, this occurs in 1 to 3 months. Filter changes depend on multiple factors, such as:

  • The kind of filter you have.
  • Children or pets in the house.
  • The season, as well as whether you live in a polluted location
  • Whether a member of the household smokes.
  • A household member who experiences asthma, allergies, COPD, or congestive heart failure
  • If you use your AC system frequently.

Plan a Regular Maintenance to Monitor Coolant Levels

During a seasonal tune-up, a trained HVAC professional conducts a thorough inspection. It includes examining coolant levels and, if necessary, charging.

A qualified HVAC technician will have the necessary measuring instruments to check levels. A non-professional should avoid handling coolant chemicals since it is a hazardous activity. Let’s all leave it to the professionals.

Get an Air Flow Examination

One of the causes of heating and cooling system failure or inefficiency is obstructed airflow. Blocked vent returns and registers restrict proper airflow, similar to clogged air filters.

As a result, your system has to work harder because there is nowhere for the cooled or heated air to go. Is there anything blocking the vents or registers? Your issue could be affected by incorrectly planned or fitted ductwork. In certain circumstances, the ductwork is installed well but is the incorrect size or capacity for your home.

Plan maintenance and ask a skilled expert to examine your air ducts and, if necessary, provide redesign alternatives. The expert will remove blockages obstructing sufficient airflow or when there is a clog, such as nesting material or other pest indications.

Clean Evaporator Coils

Your HVAC system’s drain pan or condensate lines drain excess moisture. Then the excess water freezes and gets trapped if there is a blockage. You can also have frozen HVAC coils if your pipes have frozen water in the coils.

Evaporator coils accumulate dirt, filth, and hair over time and become clogged. If moisture gets trapped inside the blockage, it will freeze, and it can cause the coils to freeze as well. A frozen coil can block the airflow and result in your system struggles or malfunctions.

Scheduling preventive maintenance is the best defense against frozen HVAC coils. You can save expenses from future AC repairs, failures, and freezing of HVAC systems if you conduct regular AC maintenance.

Final Thoughts

It’s crucial not to know what to do when your AC unit freezes up, but if you’ve read this article, we hope you’ve picked up some information about your frozen AC concerns.

Remember to schedule maintenance and keep your air conditioning system in excellent condition. Look for the warning signals that anything is off, and when you do, respond quickly to prevent further damage. A certified technician is always ready to help you!

JP Reyes

JP has been in the aircon industry for almost as long as he has been alive. As a child JP would help his tatay fix aircon units at their junk shop in Cavite. After graduating UP in the early 2000's, JP then started his own Aircon servicing business and within 5 years had 10 shops in 8 different cities. Fast forward to today and JP brings all his experience and expertise online to give readers trustworthy advice and reviews about Air-conditioning buying, servicing, cleaning and repair in the Philippines.

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