All The Reasons Why Your AC Filter Is Wet – And How To Fix Them

A wet air conditioning (AC) filter can be caused by a clogged condensate line, faulty condenser, frozen evaporator coil or a disconnected drain line. An incorrectly installed or dirty filter can also lead to a wet AC filter.

More than 90% of us use our AC units to cool us down on a daily basis during summer. A wet filter might not seem like a big issue, but if we don’t fix it quickly the underlying problem can damage our AC system, and stop them from cooling our homes.

This troubleshooting guide will take you through all the possible reasons why you have a wet AC filter, how to fix and prevent it. There’s also some information on why your filter becomes frozen, whistles, or never gets dirty.

7 Reasons For Your Wet AC Filter

1. Dirt Clogged AC Filter

You might be wondering how a dirty air filter can get wet and result in your AC leaking. It’s because a dirty filter stops air from reaching the evaporator coil of your AC unit, causing it to freeze.

When the ice melts off the coils, the drain pan will fill with water and start overflowing.

To prevent a wet AC filter, you should replace it every three months in winter and every one month or so in summer.

How to Replace a Wet AC Filter:

• Locate your thermostat and turn off the system.
• Refer to the user manual of your AC system to locate the filter if it is not obvious.
• Find a tab or slide to open the outer lid gently.
• The filter should be just below the outer cover. Reach in and pull the filter out.
• If the filter is wet and dirty, replace it with a new one.
• Locate the arrows on the filter and place it carefully inside by inserting the bottom portion first, followed by the top. Make sure that the arrows are not pointing towards you or outwards, as it will restrict the airflow. For a ceiling AC unit, arrows should be pointing upwards, and for a wall system, arrows should be pointing inside the wall.
• Fit the filter, and put the cover back.
• Tighten the fasteners to secure the system.

2. Frozen evaporator coil

A frozen evaporator coil can also cause a wet AC filter, and this might be true for you if you notice:

• AC unit turning on and off frequently without cooling the home properly
• Water surrounding the indoor AC unit
• Unusual noise from the cooling system such as hissing
• Ice build-up on your outdoor refrigerant pipes
• Vents blowing warm air

Evaporator coils allow your AC system to dehumidify and cool your home.

The dehumidifying action works by collecting moisture from the air around the evaporator coil, which then drops down to a drain pipe underlying the coil. The heat collected from the air is passed over to the evaporator coils.

As the liquid refrigerant comes in contact with heat/warm air, it transforms into gas. This cools the air quickly, with the cool air then sent into your home through the blower fan.

Why Evaporator Coils Freeze:

The evaporator coil can freeze due to:

• Dirty Evaporator Coil

If dirt accumulates on your evaporator coil, it will have a hard time absorbing heat from the air in your home. The evaporator coils get too cold and freeze over without enough heat.

• Failure of the Defrost Cycle

The defrost cycle in cooling systems keeps frost and ice from building on the evaporator coils. If the defrost cycle doesn’t run properly, the ice and frost on the coils may not be removed, causing the freezing of evaporator coils.

• Refrigerant Leak

Evaporator coils can wear out over time and develop tiny holes, causing the refrigerant to leak from your AC unit. This reduces the refrigerant level in the system, and prevents a good heat transfer from the atmosphere to the refrigerant, leading to a drop in refrigerant’s temperature.

If the refrigerant temperature drops too low, it can cause freezing of the evaporator coils. You might hear a bubbling sound from your AC unit indicating a refrigerant leak.

• Low Air Flow

If the evaporator coil doesn’t receive a consistent supply of warm air because of a clogged or blocked filter, it gets so cold to the point that it freezes the moisture collected over coils.

A large amount of moisture collected over the evaporator coil can completely cover it in ice. The water can overflow the drain pan/tray and leak when this ice melts, soaking your air filter.

How to Fix Frozen Evaporator Coils:

• Turn off your AC unit long enough so that the evaporator coils can completely thaw.
• Replace the air filter as a clogged air filter might be freezing the evaporator coils.
• If changing the filter doesn’t solve the problem, it could be a refrigerant problem that requires the assistance of a technician to resolve. Severe refrigerant leaks might require replacing the whole AC unit.

3. Faulty Condenser

Wet AC filters can be caused by a faulty or damaged condenser (also known as a compressor).

A faulty condenser will not properly condense moisture from the refrigerant. This poor condensation then leads to inappropriate evaporation. Which in turn results in the water turning back to the filter.

A condenser can fail due to the following reasons:

• Low or disrupted power supply.
• Insufficient oil. The condenser needs oil to function correctly, and a lack of lubrication can be a problem.
• Overheating caused by other system problems can increase the pressure inside the condenser

How to Fix a Faulty Condenser:

• Condenser repair is a technical and expensive procedure, and you’ll probably need the help of a technician.

For an old HVAC system, you might consider replacing the condenser as the newer models are far more efficient than the older ones.

4. Clogged condensate line

A clogged condensate line can cause a wet AC filter, and is easily diagnosed if you see:

• Water flooding around the base of your indoor AC unit
• Your outdoor condensate drain has no water flowing out
• Higher than normal indoor humidity levels
• Leaking water along with a sudden shut-off (in air conditioners with automatic water-overflow cutoff switch).

Your AC produces moisture as it runs, because it not only cools the atmosphere but also dehumidifies it.

Usually, the condensed moisture (liquid form) falls on the drip pan/tray beneath the evaporator coil, which takes the water away from the AC or HVAC system and into a drain.

The drain line can become clogged with debris, dirt, algae, or other microbial growth. When this happens the water can’t move forward and it starts accumulating in the drip pan/tray until it overflows, resulting in a wet floor or a wet AC filter.

How to Fix a Clogged Condensate Line:

If you think a clogged condensate line might be a reason for your wet AC filter. You can either contact a professional or try these steps to fix it:

• Locate the condensate drain line outside of your house. It should be near your outdoor AC unit.
• Take a standard wet/dry vac and connect it to the condensate drain pipe using a DIYvac.
• Once everything is connected, turn the wet/dry vac on for 2 to 3 minutes.
• If you detect a significant amount of debris in the wet/dry vac after this, the issue was most likely a clogged drain line. Check to see if your filter is dry, and if it is, the problem is fixed. However, if you still notice water leakage from the wet AC filter, you’ll have to check some of the other potential causes.

5. Incorrectly Installed Filter

If your AC filter is new and you notice water dripping or pooling around the base of your indoor AC unit, then it may not be properly installed.

The moisture collected by your AC system can fall directly onto the AC filter from the evaporator coils, making it damp.

You should confirm the AC unit is installed correctly before attempting to repair it.

How to Fix an Incorrectly Installed Filter:

• Remove the wet AC filter.
• Re-install the AC filter if it is in good enough condition to be used.
• Replace the AC filter if it has deteriorated from being wet.

6. Leaking Drain Pan

Cracking or rusting in a drain pan/tray is a primary reason for a wet AC filter. You’ll most likely see water collecting around your indoor AC unit if your AC filter is wet due to a leaking drain pan.

Remembering that your AC dehumidifies your home by collecting all the moisture in the drain pan, which is slowly drained out via the condensate drain line. If the drain pan is cracked, water leaks down the indoor unit making your AC filter wet (This is only true for some units and will depend on the design of your system). Due to longer moisture exposures, the drain pan gets rusted and develops cracks which then leads to more water leakage.

How to Fix a Leaking Drain Pan:

The drain pan lies just below the evaporator coil, so it isn’t easy to reach, and you might need an expert’s assistance to replace/fix it. However, if you think you’ve got the skills, buy a new drain pan compatible with your AC unit and replace the cracked one.

• Turn off the power supply.
• Remove the access panel of the AC unit, and you’ll be able to see the coils and drip pan.
• Inspect how the pan is attached in its place. Usually, it is connected either with screws or clips (If the pan is welded in place, you can’t replace it on your own; instead, you’ll have to call a HVAC technician).
• Disconnect the drip pan from the drain line using pliers or wrenches. Remove the drain pan by unscrewing or unclipping it and lift it out slowly and gently, as it might be filled with water. Avoid touching the drain pan bare-handed as it might have some mold growth.
• Insert your new drip pan and secure it with a screw or clip. Connect the drain line back to the pan.
• Close the access panel, and your AC system is good to be used again.
• You can replace the secondary drip pan in the same way. Locate the auxiliary/secondary pan at the bottom of your AC unit. Typically, it is not as tightly fixed as the primary drip pan, and you’ll just have to slide it out gently. However, unclip or unscrew it if secured by screws and clips.
• Fix your new drain pan at the right place and attach the drain pipe.
• Place the access panel back in place and turn the system on.

7. Disconnected Drain Line

The drain line connection with the air conditioner can loosen over time, causing the pipe to separate from the central system. Water seeps into your home when the drain line becomes detached.

You’ll need professional services to reconnect your drain line with the AC unit if this is the cause of your wet filter.

How A Wet Filter Can Affect Your AC System

A wet AC filter lowers an air conditioner’s efficiency, while also increasing the risk of mold and mildew growths:

Decreased Efficiency

The AC filter captures air contaminants, including debris, dirt, and pollen. A wet filter made of a tightly woven material won’t allow a proper supply of air to your AC, lowering its efficiency, possibly damaging the other internal parts, and increasing energy bills.

Increased Risk of Mold and Mildew

A wet air filter can serve as a breeding ground for microorganisms, like bacteria and molds.

How to Prevent a Wet AC Filter

Here’s how you can prevent a wet AC filter.

• The first and most important step to prevent a wet AC filter is the regular replacement of the filter.
• Always use high-quality air filters. Consult AC/HVAC experts to know the best air filter for your AC unit if you aren’t sure.
• Schedule regular maintenance with skilled technicians. This will help find any potential issues that can escalate later.

Frequently Asked Questions

Why is my AC or HVAC Filter Never Dirty

If your AC or HVAC filter is fitted incorrectly or is the wrong size, it will not become dirty. An accurately installed air filter captures all the air that passes through your air conditioner, filtering the pollutants and contaminants. If the filter is not fitted correctly, air may travel around it rather than through it, and therefore they never get dirty.

If the filter appears to be loose or too tiny, you’ll need to measure the area and select a filter that will fit snugly.

Why Your AC Filter Is Frozen

A frozen AC filter can be caused by a dirty air filter, lack of refrigerant, too many blocked or closed vents, faulty blower motor, too low thermostat, or a clogged evaporator coil. A clogged air filter is the most common reason for a frozen AC filter.

Why Your AC Filter Is Whistling

An AC filter might be whistling due to low return airflow, large debris in ducts, or a malfunctioning blower. Incorrectly configured ducts, duct leaks, closed dampers, blocked return vents, or too many closed doors can also cause a whistling sound.