Excess indoor humidity doesn’t just make the air feel heavy—it actually changes how your body perceives temperature. Based on the same principal as the heat index—an outdoor humidity calculation used to determine what’s commonly called the “feels like” temperature—excessive humidity can make an indoor environment seem warmer than it actually is. When the air is damp, sweat evaporates more slowly, so you feel warmer than the thermostat reading suggests.
How Air Conditioning Systems Handle Humidity
Air conditioners don’t just cool your air—they also play a key role in dehumidifying it. Here’s how:
- The cooling coil removes moisture. Warm indoor air passes over the system’s cold evaporator coils. As the air cools, water vapor condenses on the coil and drains away, reducing humidity.
- Temperature and humidity are connected. Cooler air can hold less moisture. When your AC runs long enough, it not only cools the air but also extracts significant moisture.
- Airflow is critical. Proper circulation ensures that the entire volume of indoor air is treated and dehumidified. Poor airflow or blocked vents reduce this effect.
When everything is working as it should, your AC keeps indoor humidity between 30–50%, which most experts recommend as the comfort zone. If your house feels sticky despite cool air, something is interfering with the process.
Common Reasons for High Humidity with the AC Running
Several issues can prevent your system from properly reducing indoor humidity:
An air conditioner that’s too large cools the home too quickly and shuts off before it can dehumidify the air. An undersized unit, on the other hand, struggles to keep up with cooling needs, leaving humidity levels high. Proper sizing is essential to comfort and efficiency.
Duct leaks can draw humid air from attics, crawl spaces, or outdoors into your system. This extra moisture circulates back into your living spaces, raising indoor humidity.
- Incorrect Thermostat Settings
If the thermostat is set too high, the AC may short cycle, turning off before enough moisture is removed. On the other hand, setting the fan to “On” instead of “Auto” can cause humid air to be blown back into the room even when the cooling cycle is not running.
- Refrigerant Issues
Low refrigerant from a leak or improper charge reduces your system’s ability to absorb heat and moisture. This can leave you with cool but clammy air.
Dirty coils, clogged filters, or blocked drains can all interfere with the system’s ability to capture and remove humidity.
6. Aging Equipment
An aging air conditioner can have trouble keeping up with demand. This doesn’t necessarily mean there are components that need replacing, just that the unit’s capability—even on a good day—isn’t what it used to be.
Effective Solutions to Improve Humidity Control
If your AC is cooling but not dehumidifying, there are several ways to improve performance:
- Adjust thermostat settings. Keep the thermostat at a steady setting and use “Auto” instead of “On” for the fan. This ensures the system cycles long enough to remove moisture.
- Use supplemental dehumidifiers. In especially humid regions or seasons, a portable or whole-home dehumidifier can work alongside your AC to maintain ideal humidity.
- Schedule regular maintenance. Cleaning coils, changing filters, and checking drain lines all help the system run efficiently and maintain its dehumidifying power.
- Seal ducts. Professional duct sealing reduces leaks that allow humid air to enter the system.
- Address refrigerant leaks. A qualified technician can test refrigerant levels and make necessary repairs, restoring cooling and dehumidifying performance.
While some steps—like adjusting thermostat settings or replacing filters—are easy fixes, persistent humidity problems usually call for professional expertise. It may be time to schedule service if you notice:
- Clammy air even when the house is cool
- Unusual noises or frequent short cycling
- Musty odors, which may signal mold growth from excess moisture
- Higher-than-normal energy bills despite steady use
An HVAC professional can evaluate whether your system is sized correctly, inspect for duct leaks, test refrigerant levels, and recommend improvements tailored to your home.
Why It Matters
Humidity control isn’t just about comfort. High indoor humidity can encourage mold growth, damage wood furniture and floors, and aggravate respiratory issues. It also forces your AC to work harder, raising energy costs. By addressing humidity problems early, you protect both your home and your health while keeping energy use in check.
When your air conditioner is cooling but not removing humidity, it’s a sign that something is out of balance. Sometimes the fix is as simple as a thermostat adjustment or filter replacement; other times, it requires a closer look from a professional. Either way, tackling the issue can transform your living space from cool and clammy to cool and comfortable—the way summer comfort is meant to feel.
This has been reviewed by Sydney Freedman, Product Marketing Manager. Sydney has more than 5 years HVAC industry experience.
