Why Is My Air Conditioner Leaking Water and What Can I Do to Fix It?

Has your air conditioner started dripping water where it never did before? Finding puddles of water around your AC unit can be puzzling and concerning. But don't worry - with the right troubleshooting, you can likely resolve the issue. There are a number of common reasons an air conditioning system can start to leak water. Identifying the underlying cause is the first step to fixing the problem or knowing when to call in a professional.

A Clogged Condensate Drain Line Can Cause Water to Back Up

The condensate drain line carries water away from the evaporator coils and out of your home. Over time, it can become clogged with dirt, dust, mold and other debris. When the drain line is blocked, water can't properly drain and will start to back up. This can cause leaks inside your home around the air handler or other areas of the AC system.

Signs of a clogged condensate drain line include:

Water pooling around the air handler or furnace
Leaks along the drain line path
Visible mold growth around drain line
Musty odor coming from drain line area

If you notice these issues, try pouring a drain cleaner down the line to break up blockages. You can also use a stiff wire or small snake to loosen debris. Make sure any slip joints are tightened. If simple solutions don't work, call an HVAC technician to diagnose and clear the drain line fully. Allowing the issue to persist can lead to water damage or mold growth in the home.

A Frozen Evaporator Coil Can Cause the AC System to Leak

The evaporator coil is responsible for absorbing heat from the air as a key part of the air conditioning process. But if something causes the coil to freeze over, it can lead to water leaks. A frozen evaporator coil happens when the coil gets too cold due to problems like:

Faulty thermostat - If the thermostat malfunctions and under-reads the room temperature, it will signal the AC unit to keep pumping out excessively cold air. This over-cooling causes ice to build up on the coils.
Dirty air filter - A clogged, dirty air filter restricts proper airflow. This can cause the evaporator coil to freeze up.
Low refrigerant - Not having enough refrigerant can prevent the evaporator coil from getting sufficiently cold. The coil then starts to freeze over in an attempt to get colder.
Poor airflow - If airflow is obstructed due to a blocked vent or dirty blower fan, it can also lead the coil to freeze.

No matter what causes it, a frozen evaporator coil can't operate properly. As it tries to keep cooling, ice will melt and drip out water around the unit. Signs your coil may be frozen include:

Reduced airflow from vents
Unusual noises from the unit
Water pooling below the coils
Frost buildup on the coils

Try turning your AC off for 24 hours and letting the coil naturally thaw. You can also set the fan to ON to blow air over the coil. But if those tactics don't resolve it, call an HVAC pro to safely diagnose and fix the issue. A technician can check the refrigerant level, thermostat calibration, airflow and more to get your AC running right again.

A Leaky or Rusted Drain Pan Can Cause Water Drips

The drain pan is located under the evaporator coil to collect condensation produced during cooling. This water then flows out of the pan through the condensate drain line. But if the drain pan has any cracks, holes or rust spots, it can start to leak water inside the ductwork and home.

Some signs of a leaking drain pan are:

Water dripping from the ductwork joints
Wet spots on walls or ceiling below the AC unit
Water pooled under the air handler or furnace

Try tightening the pan bolts or sealing any small cracks with HVAC metal tape. For larger holes or extensive rusting, the entire drain pan may need replacement. An HVAC technician can determine if replacement is needed and install a new drain pan. Catching a leaking drain pan early is important to prevent mold growth in the HVAC system.

Damaged Condenser Coils Can Result in Refrigerant Leaks

The condenser coils in your outdoor AC condenser unit release heat from the refrigerant as part of the cooling process. But damage to these coils can cause refrigerant leaks. Common ways condenser coils get damaged include:

Being struck by lawn equipment like a weed trimmer
Being hit by falling debris or rocks
Vibration from an improper or loose installation
Corrosion from exposure to the outdoor elements

Refrigerant leaks can cause a number of problems:

Low refrigerant levels mean the AC system can't cool properly, forcing the evaporator coil to freeze up and leak water.
The leak may allow air and moisture into the sealed system, further reducing cooling efficiency.
Refrigerant itself can leak out rapidly in a hissing noise.

If you suspect your condenser coil is damaged and leaking refrigerant, it's important to have an HVAC technician inspect it right away. They can check for leaks using specialized tools and fluorescent dye. Damaged coils need to be repaired or replaced. The technician will also recharge the system with refrigerant after fixing any leaks. Taking quick action prevents refrigerant loss from worsening and requiring a full system replacement.

Malfunctioning Thermostats Can Lead to Frozen Evaporator Coils

Your thermostat is the "brain" of your AC system, telling it when to pump out cool air to reach the desired temperature. But if the thermostat malfunctions, it can give incorrect signals and cause a frozen evaporator coil. Here's how:

Faulty temperature sensor - If the thermostat's temperature sensor is off, the reading it gives your AC system will be inaccurate. This leads to over-cooling and coil freeze up.
Electrical issue - Problems with the thermostat's internal wiring can cause strange temperature readings and signals. The AC unit then overcompensates trying to reach the right temp.
Power surge - Electrical surges from storms or grid issues can short out the thermostat's components and disrupt normal operation.
Low batteries - If the thermostat has weak batteries, it can glitch and give false readings to the AC system.

A frozen evaporator coil will start to leak water in these cases. Other signs of a faulty thermostat include:

AC running non-stop without reaching set temp
AC not turning on even though too warm
Display problems or error messages

Replacing the thermostat should resolve these types of issues. A technician can install a new digital or smart thermostat tuned to your AC system's specifications. This inexpensive repair prevents expensive AC damage from a frozen coil.

Clogged Condensate Drain Lines Cause Backups

Earlier we discussed how a clogged condensate drain line inside the home can cause water leaks. But a clogged condensate line running outside can also create water backup issues. This exterior drain line carries water away from the condenser unit during heat mode. If it gets blocked, water can overflow from the AC system.

Causes of clogged exterior drain lines include:

Dirt, leaves and other debris
Mold or algae growth
Insects nesting in the line
Improper slope that prevents drainage

Signs of a clogged exterior drain line are:

Standing water around the condenser unit
Water leaking from the base of the unit
Reduced AC performance and freezing coils

Use a small auger or wire to try clearing debris from the outdoor line. Check the slope and integrity of the line. If simple DIY efforts don't work, call an HVAC company to fully clear any stubborn clogs. They can also replace any damaged drain line sections.

How to Thaw a Frozen Evaporator Coil

If you realize your evaporator coil has frozen over and caused water to leak, taking prompt action can get your AC running properly again. Here are tips to safely thaw a frozen AC coil:

Turn Off the Air Conditioner

Don't run your AC system while the evaporator coil is still frozen! This can worsen damage to the compressor and other components. Turn the system off at the thermostat or the outside condenser unit.

Let the Coil Naturally Defrost

With the AC shut off, leave the frozen coil alone for 6-12 hours. In warmer weather, it may naturally defrost on its own in this time. The key is to allow the ice to melt without any forced airflow over it.

Set the Fan to ON

If the coil doesn't thaw after 12 hours, set your thermostat's fan to the ON position for continuous airflow over the coil. Make sure the AC remains off. The constant air movement will help melt any remaining ice.

Check and Change the Air Filter

A restricted air filter is a common cause of evaporator coils freezing up. While the AC is off, check your filter and change it if dirty. Insert a clean filter to prevent future freeze ups.

Ensure the Coil is Fully Dry

Once thawed, the coil should be dried completely before turning the AC back on. Water left on the coil can freeze again or get blown into ducts. Wipe down any condensation with a towel. You may need to leave the fan running for several hours.

Monitor Operation When Restarting

When you restart your AC, keep an eye and ear out for any signs the coil is refreezing, like reduced air flow or odd sounds. Immediately turn off the unit if you notice ice buildup starting again.

Calling a technician is highly recommended if you can't get the coil fully thawed on your own. They have specialized tools and methods to safely thaw frozen AC coils. Repairing any underlying issues, like refrigerant leaks or airflow problems, is key to preventing a repeat freeze up.

When to Call an HVAC Technician for AC Leaks

While some minor AC leaks may be DIY-fixable, more serious issues require a professional HVAC technician's expertise. Call a technician right away if you experience:

Significant or rapidly leaking water
Leaks you can't trace to an obvious source
Signs of a frozen evaporator coil
Strange noises from the AC system
Reduced cooling and airflow

A qualified technician has the training, skills and tools to properly:

Diagnose the root cause of water leaks
Inspect, repair or replace a clogged drain line
Thaw a frozen AC coil safely
Fix refrigerant leaks and recharge refrigerant
Replace a leaky drain pan
Repair a damaged condenser
Install a new thermostat

Don't delay calling an HVAC company if you notice water pooling around your AC unit or other troubling signs. The sooner the problem is fixed, the less risk of severe damage or mold growth in your home. With prompt repair, your newly leak-free AC system will be ready to keep you comfortable all summer long!