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What Causes AC Pipes To Freeze?

Ac Cooling Air Pipes Covered By Snow Or Frozen

Air conditioners are perfect for keeping your house cool on hot summer days. However, you can be worried when the ice starts forming on your climate control unit.

So, why do your AC pipes freeze up? Though frozen aircon systems might be surprising, it is a common phenomenon. It indicates that something is wrong with your appliance and requires immediate attention.

We will examine what is wrong with your air conditioner, leading to the frozen pipes. In addition, we also offer a comprehensive guide on how to fix the issue.


The AC pipes might be freezing due to obstructed airflow caused by a clogged air filter, evaporator coil, fan, drain pan, and vents. A defective thermostat, fan motor, and refrigerant pipes can also be another cause of the problem.

Are you worried about your AC pipes freezing up? Stick around to learn more about the problem and how to fix it.

8 Reasons Your Air Conditioner Pipes Freeze Up

Several reasons can cause your HVAC pipes to freeze. Before fixing the issue, it is critical to identify the cause to prevent further damage to your unit and expensive repairs down the road.

Here are some possible reasons why your central AC pipes may be freezing:

1. Dirty Air Filter

Cleaning Ac Dirty Air Filter

A dirty air filter is one of the first things you should check if your aircon pipes are frozen.

The air filter is responsible for removing dirt, dust, debris, and other contaminants from the air circulating from the system into the room.

When the filter becomes clogged, it affects the efficiency and performance of your climate control appliance. It restricts the circulation of airflow into the device. Ice can start forming if warm air does not reach the evaporator coils, leading to freezing.

Cleaning a Clogged Air Filter

Ensure you turn off the appliance before removing the filter for cleaning.

Unclogging the air filter depends on which type of filter is installed. Some can be washed with water and mild detergent, while others can only be vacuumed or brushed.

Always check your user manual for the appropriate method to clean your filter.

Useful Tip

Ensure you clean your air filter regularly to prevent the air conditioner from freezing or wearing out. In addition, the filter should be replaced after 4-5 months.

2. Clogged Evaporator Fan

Air Conditioner Outdoor Unit

A clogged evaporator fan can also cause the HVAC tubes to freeze up.

The AC evaporator fan is responsible for air circulation in the unit. The fan pulls in warm air from the room, runs it across the evaporator coils, where it is cooled, and then pushes cool air out. In the process, the warm air defrosts any ice on the coils.

However, clogged or blocked evaporator fans are less effective in circulating air across the coils. As dirt or debris accumulates around the fan blades, it causes resistance in their spin. Lower fan speed encourages lower airflow leading to the coils freezing.

How To Fix a Clogged Evaporator Fan

Turn off the AC and remove the indoor unit’s front panel or access cover. Check for any dirt or debris that can prevent the blades from spinning.

Use a soft brush or cloth to remove dirt accumulation. Apply gentle pressure when cleaning to avoid damaging or bending the blades.

Damaged Fan

If the fan or blade is damaged, it should be replaced. Always replace the fan with an original equipment manufacturer (OEM) part.

3. Leaking Refrigerant Pipes

The Air Conditioner Has Leaks Of Refrigerant

Low refrigerant levels can also be the culprit.

The refrigerant fluid cools the air coming into the air conditioner by absorbing heat from the air inside the room.

However, if your refrigerant is leaking, your AC struggles to transfer the heat throughout the unit, causing the evaporator coils to get cold. Over time, frost forms around the coils, causing the appliance’s pipes to freeze.

Likewise, leaking refrigerant makes a sizzling or hissing sound as fluid escapes.

Repairing Leaking Refrigerant Pipes

Refrigerant fluid is poisonous, and exposure can cause vomiting, headaches, nausea, skin and eye irritation, and breathing problems. An HVAC repair professional should repair broken or cut aircon pipes immediately.

4. Faulty Thermostat

Adjusting Temperature From The Ac Settings

A defective thermostat might also be why your air conditioning pipes are frozen.

You can think about the thermostat as the brain of your AC unit. It tells the system when and how long it should run to reach the ideal temperature for the room. When this temperature is achieved, the thermostat turns off the unit, and the room gets warm again.

However, a defective thermostat on your portable or window AC has a problem regulating the temperature in the unit. Even after achieving the desired temperature, the system continues cooling down, leading to ice formation around the pipes.

Fixing a Defective Thermostat

There are several reasons why your thermostat might not be working. Before troubleshooting or replacing it, you should identify the reason for the problem.

Your best bet is to call a repair expert to look at the thermostat.

5. Dirty Evaporator Coil

Ac Dirty Evaporator Coil

Another reason for the frozen AC pipes is a dirty evaporator coil.

The evaporator coil is responsible for heat transfer between the refrigerant and outside air. The coil sits on the evaporator behind the fan.

If dirt and dust get past the air filter and fan, they can find their way to the coils. When the dirt accumulates, it creates a layer that prevents adequate heat transfer in the unit. Because warm air does not reach the coils, frost can quickly form around the coils, leading to frozen pipes.

How To Clean the Evaporator Coil

Cleaning the evaporator coil in your aircon unit is more complex than you might think. We recommend letting a qualified professional handle it.

6. Defective Fan Motor

Hvac Unit Motor Belt Drive

It is also possible that the fan motor in your air conditioner is broken.

A motor powers the evaporator fan, and a defective motor reduces air circulation to the coils, reducing the unit’s heat transfer effectiveness. Likewise, if the motor has a low spin speed, it can have issues drawing in enough air to warm the coils.

It results in the build-up of ice along the AC pipes, potentially leading to freezing up.

How To Repair a Broken Fan Motor

Sadly, faulty fan motors should be replaced. Continued use of the motor can lead to further damage to the unit and be a handful to repair later. Always call a professional AC technician if you have a broken motor.

Helpful Tip

To ensure better aircon efficiency and longevity, replace the motor with a genuine part recommended for your model.

7. Clogged Drain Pipe or Pan

Clogged Drain Pipe

The climate control unit might also need to be drained to stop the pipes from freezing.

Unlike self-evaporating AC units that release condensed water outside the room, standard units have a drain pan or drain pipe that collects water dehumidified from the room. The pan or tube needs to be regularly emptied to prevent water from accidentally leaking or freezing up in the HVAC.

How To Fix a Clogged Drain Pipe or Pan

The best way to deal with the issue is by turning off the unit and waiting for it to defrost. You can run hot water through the pan to remove any ice or dirt stuck in the pan or tube.

8. Blocked Aircon Vents

Dirty And Blocked Aircon Vents

Lastly, having a blocked vent can also cause the AC pipes to freeze.

The vents in your air conditioner provide air circulation to the unit. When the vents are obstructed, the air conditioner does not have proper airflow, leading to ineffective heat transfer.

Fixing Blocked AC Vents

Check if the vents around the house have any obstructions. Clear the vent entrance to ensure better airflow circulation if any vents are blocked or obstructed.


An air conditioner is expensive, and finding frost build-up on the unit can be a bit worrying. That is why regular maintenance should be a top priority to ensure the device works efficiently and for a longer time.

However, if your AC pipes are frozen, you likely have a problem with a clogged or blocked evaporator fan, coil, or air filter. Furthermore, a thermostat malfunction, defective fan motor, and low refrigerant levels can also be the problem.

Lastly, the frosted pipes may result from a clogged drain pipe, pan, or blocked vent.

Frequently Asked Questions

How Do You Keep Your Air Conditioner Lines From Freezing?

The best way to prevent your AC lines from freezing is by identifying the cause of the issue. The culprits are often clogged vents, air filters, fans, or coils. In addition, malfunctioning parts like the thermostat, refrigerant pipes, and fan motors can also be an issue.

Can a Dirty Air Filter Cause the AC To Freeze?

The short answer is yes! The air filter feeds warm air to the evaporator coils for cooling. In the process, any ice that forms on the coils is thawed. However, if the AC filter has dirt, it prevents proper air circulation, leading to ice formation.

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