AC Is Cooling But Not Removing Humidity? 6 Causes (Ranked by Frequency)

Your air conditioner is running, the house feels cool, but something's off. The air still feels sticky, your windows are fogging up, and maybe you've even noticed a musty smell developing. If your AC is cooling but not removing humidity, you're dealing with one of the most common and misunderstood HVAC problems we see in North Georgia homes.

For over 25 years, our family-owned team at MR. HVAC has diagnosed thousands of humidity issues across Canton, Woodstock, Roswell, and Alpharetta. Georgia's humid subtropical climate makes this problem especially common here. The good news? We'll explain exactly how your AC removes humidity (it's not what most people think), walk through the six most common causes ranked by how frequently we encounter them, and help you identify which issue you're likely facing.

How Your AC Actually Removes Humidity (The Part Most Homeowners Miss)

Here's what most homeowners don't realize: your air conditioner does two separate jobs simultaneously. It cools the air AND removes moisture. These functions can fail independently, which is exactly why you can have a house that's cool but still feels clammy.

Dehumidification occurs at your evaporator coil (the indoor coil). When warm, humid air from your home passes over this cold coil, two things occur. First, the air temperature drops. Second, moisture in the air condenses on the coil surface, as water droplets form on a cold glass of water on a summer day. This condensed water then drips into a drain pan and exits your home through the condensate line.

For proper dehumidification, three conditions must be met:

• The evaporator coil must be cold enough to cause condensation
• Air must spend enough time passing over the coil for moisture to condense
• The condensate must drain properly away from the system

When any of these conditions isn't met, your AC will cool the air without adequately removing humidity. Understanding this distinction is key to diagnosing the problem.

Quick Diagnostic Guide: Identify Your Issue

Use these questions to narrow down the likely cause:

• Has the problem existed since the AC was installed? If yes, suspect an oversized unit.
• Did the problem develop gradually over time? Likely a dirty coil or developing refrigerant leak.
• Is your thermostat fan set to "ON"? Switch to "AUTO" and monitor for 24 hours.
• Do you see ice on refrigerant lines or the coil? Points to low refrigerant or severely restricted airflow.
• Is there standing water near the indoor unit? Check for a clogged condensate drain.
• Are some rooms more humid than others? Suggests ductwork issues.
• Does your AC run in short cycles (under 15 minutes)? Classic sign of an oversized system.

6 Causes Your AC Is Cooling But Not Removing Humidity (Ranked by Frequency)

Based on our service calls across North Georgia, here are the most common culprits, ranked by how often we encounter each one.

1. Dirty Evaporator Coil (40% of Cases)

What's happening: When dust, dirt, and debris accumulate on your evaporator coil, they form an insulating layer that prevents proper heat and moisture transfer. The coil can still cool air somewhat, but it can't get cold enough to effectively condense humidity out of the air.

Why it occurs: North Georgia's pollen seasons (we get hit twice a year) accelerate coil contamination. Homes with pets, older ductwork, or inconsistent filter changes are most likely to experience this problem. The coil sits in a dark, damp environment, and once debris sticks, it tends to accumulate quickly.

Signs you're dealing with a dirty coil:

• Humidity problems developed gradually over months
• AC runs longer than it used to
• Airflow from vents feels weaker
• You haven't had professional maintenance in over a year
• Visible dust or buildup on the coil (if accessible)

The solution: Professional coil cleaning restores proper heat transfer and dehumidification capacity. This isn't a DIY job. The evaporator coil requires specialized cleaning solutions and careful handling to prevent damage to its delicate fins. Our certified HVAC technicians can thoroughly clean your coil and inspect for any related issues during the same visit.

2. Oversized AC Unit (25% of Cases)

What's happening: An oversized air conditioner cools your home too quickly. While that might sound like a good thing, it creates a major problem for dehumidification. The system reaches the thermostat's target temperature before the air has spent enough time passing over the evaporator coil to remove adequate moisture.

Why it occurs: This usually stems from improper sizing during installation. Some contractors use rule-of-thumb calculations instead of performing a proper Manual J load calculation. Others deliberately oversize units, thinking "bigger is better" or to avoid callbacks about cooling capacity. Unfortunately, an oversized system will struggle with humidity for its entire lifespan.

Signs your AC is oversized:

• System runs in short cycles (10-15 minutes on, then shuts off)
• The house cools down very quickly
• Humidity problems existed since installation
• Temperature swings feel dramatic between cycles
• Energy bills are higher than expected

The solution: Long-term, the right fix is properly sizing your next system when it's time for replacement. In the meantime, upgrading to a variable-speed or two-stage system, adding a whole-house dehumidifier, or adjusting fan settings can help manage symptoms. A professional AC assessment can determine whether your system is oversized and recommend the most cost-effective solutions.

3. Low Refrigerant Levels (15% of Cases)

What's happening: Refrigerant (the chemical that absorbs heat) is essential for both cooling and dehumidification. When levels drop due to a leak, the evaporator coil can't get cold enough to effectively condense moisture from the air. You might notice a drop in cooling capacity as well, but humidity issues often appear first.

Why it occurs: Refrigerant doesn't get "used up" like fuel. If levels are low, there's a leak somewhere in the system. Common leak points include the evaporator coil, condenser coil, refrigerant lines, and service valve connections. Leaks can develop from vibration, corrosion, or manufacturing defects.

Signs of low refrigerant:

• Ice forming on refrigerant lines or the evaporator coil
• Hissing or bubbling sounds near the indoor unit
• Cooling and dehumidification are declining together
• Higher energy bills without increased usage
• System running constantly without reaching the set temperature

The solution: Simply adding refrigerant without fixing the leak is a temporary patch that wastes money and harms the environment. A proper repair involves locating the leak using electronic detection or dye testing, repairing the leak point, and then recharging the system to manufacturer specifications. This requires professional diagnosis and AC repair by EPA-certified technicians.

4. Incorrect Thermostat Fan Setting (10% of Cases)

What's happening: When your thermostat fan is set to "ON" instead of "AUTO," the blower runs continuously, even when the compressor isn't cooling. This constant airflow actually re-evaporates moisture that collected on the evaporator coil and blows it right back into your home.

Why it occurs: Some homeowners set the fan to "ON" thinking it will improve air circulation or filtration. While continuous fan operation does circulate air more evenly, the humidity tradeoff often isn't worth it, especially in Georgia's climate.

Signs the fan setting is the issue:

• The thermostat fan is set to "ON" rather than "AUTO"
• Humidity feels worse during periods when AC cycles off
• The problem resolves quickly when the fan is switched to "AUTO"

The solution: Switch your thermostat fan setting from "ON" to "AUTO." In AUTO mode, the fan only runs when the system is actively cooling, allowing moisture to properly drain from the coil between cycles. If you prefer continuous air circulation, consider adding a whole-house dehumidifier to compensate or upgrading to a smart thermostat with humidity control features.

5. Clogged Condensate Drain (7% of Cases)

What's happening: The condensate drain line carries moisture removed from your air out of the system. When this line becomes clogged with algae, mold, or debris, water backs up into the drain pan. Some systems will shut down as a safety measure; others keep running but can't effectively remove humidity because the drainage path is blocked.

Why it occurs: The condensate drain is a perfect environment for biological growth. It's dark, wet, and warm. Georgia's humidity accelerates this process. Without regular maintenance, algae and slime build up inside the drain line until water can't pass through.

Signs of a clogged drain:

• Water pooling around the indoor unit or in the drain pan
• Musty or moldy smell near the air handler
• AC shuts off unexpectedly (if equipped with a float switch)
• Water stains on the ceiling below attic-mounted units

The solution: The drain line needs to be cleared and flushed. While some homeowners attempt this with a wet/dry vacuum or vinegar flush, stubborn clogs often require professional equipment. Regular maintenance, including drain line treatment, prevents this problem from recurring.

6. Leaky or Poorly Insulated Ductwork (3% of Cases)

What's happening: When ducts leak or lack proper insulation, especially in unconditioned spaces like attics, two humidity problems occur. First, humid outside air infiltrates the system through leaks. Second, cold supply air passing through hot attic spaces causes condensation on duct exteriors, which can drip and create moisture issues.

Why it occurs: Ductwork degrades over time. Connections loosen from vibration and temperature cycling. Insulation compresses or falls away. In North Georgia, attic temperatures can exceed 130°F in summer, creating extreme temperature differentials that stress duct systems.

Signs of duct problems:

• Some rooms feel more humid than others
• Visible condensation on ductwork in the attic
• Dusty conditions despite regular filter changes
• Uneven temperatures throughout the house
• Higher than expected energy bills

The solution: Duct sealing and insulation improvements address this issue. Professional duct testing can quantify the amount of air your system is losing and identify the most problematic areas. Sealing leaks and adding insulation not only improves humidity control but also increases overall system efficiency.

Why Fixing This Matters

High indoor humidity isn't just uncomfortable; it's also harmful. It creates real problems for your home and health:

• Mold and mildew growth: Humidity above 60% creates ideal conditions for mold, especially in bathrooms, closets, and areas with poor air circulation
• Dust mite proliferation: These microscopic allergens thrive in humid environments and are a leading cause of indoor allergy symptoms
• Structural damage: Excess moisture can warp wood floors, damage furniture, peel paint, and compromise building materials over time
• Higher energy costs: Humid air feels warmer, leading many homeowners to lower thermostat settings and run AC longer than necessary
• Electronics and instrument damage: Excess moisture can harm computers, musical instruments, and other sensitive equipment

When to Call a Professional

While checking your thermostat setting is a quick DIY fix, most humidity issues require professional air conditioning service to properly diagnose and resolve.

Contact a certified HVAC technician if:

• Humidity problems persist after switching the fan to "AUTO"
• You see ice forming anywhere on the system
• There's standing water near the indoor unit
• The system hasn't been professionally maintained in over a year
• You suspect refrigerant issues (hissing sounds, declining performance)
• You're considering a new system and want proper sizing
• Indoor humidity consistently reads above 55-60% on a hygrometer

With over 25 years of experience serving North Georgia families, we've diagnosed and resolved thousands of humidity problems. Our technicians have the tools and training to quickly identify the root cause, whether it's a dirty coil, a refrigerant leak, or a system sizing issue.

The Bottom Line

When your AC is cooling but not removing humidity, the most likely culprits are a dirty evaporator coil (40% of cases) or an oversized system (25% of cases). If this is happening to you, start by checking your thermostat fan setting. If it's set to "ON," switch it to "AUTO" and give the system 24 hours.

If that doesn't solve the problem, or if you notice any warning signs like ice formation, water leaks, or declining cooling performance, it's time for a professional diagnosis.

Contact MR. HVAC for professional AC repair and humidity diagnosis in Canton, Woodstock, Roswell, Alpharetta, and throughout North Georgia.

Frequently Asked Questions

Why is my house humid even with the AC running?

Your AC removes humidity through condensation on the evaporator coil, but this process can fail even while the cooling continues working. The most common causes are a dirty evaporator coil that can't get cold enough, an oversized system that cycles too quickly, or low refrigerant levels. Check your thermostat fan setting first. If it's set to "ON," switch to "AUTO" since continuous fan operation re-evaporates moisture back into your home.

What humidity level should my house be?

Indoor humidity should stay between 30-50% for optimal comfort and health, though up to 55% is acceptable. Above 60% creates conditions favorable to mold growth, dust mites, and that sticky, uncomfortable feeling. You can monitor humidity with an inexpensive hygrometer from any hardware store. If your AC can't maintain proper humidity levels even when running normally, there's likely an underlying issue that requires professional attention.

Can a dirty air filter cause humidity problems?

Yes. A severely clogged filter restricts airflow across the evaporator coil, which can cause the coil to freeze up and stop dehumidifying effectively. It also allows more dust and debris to reach the coil itself, contributing to the buildup that's the number one cause of humidity problems. Replace your filter every 1-3 months, depending on your home's conditions, more frequently if you have pets or allergies.

Will a bigger AC unit remove more humidity?

No. In fact, the opposite is true. An oversized AC cools your home so quickly that it doesn't run long enough to adequately dehumidify the air. This is called "short cycling." The system satisfies the thermostat before moisture can condense and drain from the evaporator coil. Proper sizing based on a Manual J load calculation ensures your system runs long enough to both cool and dehumidify effectively.