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A Complete Guide to Finding and Fixing AC Leaks

June 12, 2024

Why isn’t your room as cool as it used to be even though the AC is cranked up? If you’ve noticed warm air blowing out instead of being crisp and cool, chances are you’ve got a leak somewhere in your AC system. The good news? Most AC leaks can be fixed with some know-how and elbow grease. 

In this complete guide, we’ll cover how to identify the signs of an AC leak, track down the source of the problem, and walk you through DIY solutions for fixing water and air leaks. We’ll also explore when to call in a pro for those tricky refrigerant leaks.

5 Common Signs of an AC Leak

If your air conditioner develops a leak, it will likely show some telltale signs. Here are some common indicators that your AC unit has sprung a leak:

  1. Reduced Cooling Power: One of the first things you’ll probably notice with a refrigerant leak is that your AC isn’t cooling like it used to. As refrigerant levels drop, the system loses its ability to remove heat effectively from your home’s air.
  2. Frozen Evaporator Coils: Look at the indoor portion of your AC unit. If you see ice buildup on the evaporator coils, it’s often because there isn’t enough refrigerant to absorb heat properly. The excess moisture then freezes on the coils.
  3. Hissing or Bubbling Sounds: Refrigerant leaks can cause hissing or bubbling noises as the liquid or vapor escapes from holes or cracks in the AC components. Listen carefully near the compressor unit when the system is running.
  4. Moisture or Residue Around Unit: Visible moisture or residue around your AC’s indoor or outdoor portions can indicate a few different types of leaks. Water could be dripping from a clogged condensate drain. You may also see oily residue if the refrigerant leaks out.
  5. Higher Energy Bills: An unexpected spike in your utility costs can sometimes be traced back to your AC unit having to work harder due to low refrigerant levels from a leak.

Potential Causes of an AC Leak

There are a few common culprits that can cause AC leaks:

Refrigerant Leaks

  • Cracks or holes in the refrigerant lines due to wear, corrosion, or physical damage
  • Leaks around the connections and fittings where lines are joined
  • Failed compressor valves or seals allowing refrigerant to escape
  • Leaks in the evaporator or condenser coils from manufacturing defects or corrosion

Water Leaks

  • Clogged or broken condensate drain lines not allowing moisture to drain properly
  • Cracked or rusted condensate drain pans causing water to overflow
  • Leaks around the drain line connections coming loose
  • Improper installation leading to condensate drainage issues

Air Leaks

  • Gaps, cracks, or disconnections in the ductwork letting conditioned air escape
  • Damaged or deteriorated duct insulation allowing cooled air to be lost
  • Leaks around windows, doors, or other home entry points
  • Improperly sealed AC unit casings or access panels

Age and lack of maintenance are often contributing factors, as AC components can degrade over time. Minor leaks can then turn into bigger problems if not addressed promptly.

Why AC Leaks Are a Major Concern

While a leak may seem like a minor annoyance at first, allowing it to persist can lead to several serious issues:

Decreased Energy Efficiency and Higher Utility Costs 

As refrigerant levels drop due to leaks, your air conditioner has to work harder and run longer cycle times to achieve the same cooling output. This increased energy consumption shows up on your utility bills—according to the U.S. Department of Energy, a mere 10% reduction in refrigerant levels can increase operating costs by 20%.

Premature System Failure and Expensive Repairs 

When an AC unit keeps running with low refrigerant caused by a leak, it puts excessive strain on components like the compressor. This can burn out the compressor or other parts much sooner than their expected 12–15-year lifespan. Replacing a compressor can cost up to $1,500 for labor and materials.

Mold Growth and Structural Damage

Leaks that allow condensation or refrigerant to escape can create dampness issues. Water leaking into walls, ceilings, or floors promotes mold and mildew growth that is difficult to fix. Beyond potential health effects, mold can cause structural damage by degrading wood, insulation, and drywall over time.

Reduced Indoor Air Quality Impacting Health

Refrigerant leaks may release harmful gasses into the air you breathe. Even small amounts of certain refrigerants can cause respiratory issues, nausea, or more severe health effects with long-term exposure. Mold growth from moisture leaks also degrades indoor air quality.

Safety Hazards Like Fire Risks or Electrical Shocks

Some AC leaks also pose physical safety concerns. A combustible refrigerant leak near electrical systems creates a fire hazard. Leaks around electrical components may also increase the risk of shocks or burns if water contacts live wires or circuits.


Broken AC


Finding the Source of the AC Leak

Finding the exact source of an AC leak can be tricky, but here are some tips and methods:

  • Visual Inspection: Start by doing a thorough visual check of the entire AC system—indoor and outdoor units, refrigerant lines, drain lines, ducts, etc. Look for any signs of moisture, refrigerant residue, or damaged components.
  • Soap Solution Test: Mix up a diluted soap and water solution. Apply it along refrigerant line connections, coils, and other components where a leak may occur. Watch for bubbles forming, indicating air escaping and pinpointing the leak location.
  • UV Dye Test: UV dyes can be introduced into the system and allowed to circulate to detect refrigerant leaks. The dye glows under UV light, making even small leaks easily visible when inspected with a blacklight tool.
  • Electronic Leak Detectors: Professionals have access to electronic refrigerant leak detectors. These highly sensitive devices can sniff out the minutest traces of escaped refrigerant in the air around an AC system.
  • Nitrogen Pressure Test: The system is pressurized with nitrogen gas instead of refrigerant. Technicians can then check for any nitrogen escaping to reveal leak points.
  • Following the Trail: Look for telltale signs like dust accumulation patterns on components, oil residue streaks or trails, or corrosion, which can indicate where a leak originated.

The specific method used may depend on whether you’re dealing with a suspected refrigerant, water, or air leak. Refrigerant leaks, in particular, often require professional equipment and expertise to locate accurately.

How to Fix AC Leaks (DIY Solutions and When to Call a Pro)

Fixing Refrigerant Leaks

A certified professional HVAC technician should always handle refrigerant leaks. Attempting DIY repairs with refrigerants is extremely dangerous as they are toxic and combustible. Here are the typical steps for fixing a refrigerant leak:

  • Leak Detection – Using methods like electronic detectors, dye tests, etc., to precisely locate the source of the leak. 
  • Repair/Replacement – Once the leak point is identified, the faulty component, such as a coil, valve, or refrigerant line, needs repair or full replacement. 
  • System Evacuation – The existing refrigerant is carefully vacuumed out of the system using specialized equipment. 
  • Leak Testing – After repairs, the system is pressure tested to ensure there are no other remaining leaks. 
  • Recharging – Finally, the AC is recharged and filled with the proper amount and type of refrigerant specified by the manufacturer.

Fixing Water Leaks

Many water leaks from an AC system can be repaired yourself if you feel comfortable. Always shut off the unit’s power first.

Condensate Drain Line Clogs:

  1. Locate the drain line access point near the inside air handler unit.
  2. Use a wet/dry vacuum or compressed air to clear out any built-up debris or algae growth restricting drainage.
  3. Pour a mix of water and vinegar through to help flush the line.

Drain Pan Leaks:

  1. Remove access panels to inspect the condensate drain pan under the indoor coil.
  2. Use a wet/dry vacuum to drain any standing water.
  3. For a crack, seal with an HVAC-approved sealant.
  4. For excessive damage or corrosion, replace the drain pan entirely.

Fixing Air Leaks

Duct Leaks:

  1. Locate any obvious gaps, cracks, or disconnected ductwork runs using a flashlight.
  2. Seal smaller holes and seams using foil tape or mastic sealant rated for ducts.
  3. For larger gaps, use rigid duct sealant or replacement duct sections.

Cabinet/Window Leaks:

  1. Locate cracks or drafty entry points around the AC cabinets or window units.
  2. Use a latex or silicone-based caulk to properly seal any openings.
  3. For window units, check the accordion panels are properly sealed against the window frame.


AC Maintenance and Leak Prevention

While fixing a leak is an important reactive step, proactive AC maintenance is vital to preventing leaks in the first place. 

The Importance of Regular AC Maintenance

Having an HVAC professional perform routine maintenance on your air conditioning system, usually once a year before peak cooling season, is crucial for preventing leaks down the road. During these tune-ups, the technician will:

  • Inspect all components and connections for any wear, cracks, or impending leaks.
  • Check refrigerant levels and test for any existing refrigerant leaks.
  • Clean coils and clear drain lines to prevent clogs that can lead to water leaks.
  • Tighten fittings and replace worn parts that could eventually spring a leak.

Note: Even tiny leaks can slowly worsen without proper maintenance. 

Tips for Preventing Future AC Leaks

In between professional services, there are some simple DIY tasks to prevent leaks:

  • Change air filters regularly (monthly for peak seasons).
  • Straighten any bent refrigerant lines to prevent rubs/leaks.
  • Clear away any vegetation growing too close to the outdoor unit.
  • Inspect and clean condensate drain lines periodically.
  • Use HVAC foaming cleaners to service the coils yourself.
  • Schedule chemical washes if dirt builds up on the coils.
  • Fix any insulation duct leaks to prevent moisture problems.

With proper maintenance and some basic homeowner care, you can prevent many potential leak issues and keep your AC running strong for years. A little preventative effort goes a long way!