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High Humidity Inside With AC Running
in Sioux Falls, SD
Sioux Falls sees humid stretches through July and August that make indoor air feel heavy and uncomfortable. Your AC is supposed to pull that moisture out of the air as it cools the home. When it stops doing that well, rooms feel damp and sticky even when the temperature reads normal. Persistent high humidity also promotes mold growth, especially in basements and older homes with less air circulation.
Quick Answer
If your AC is running but the house feels humid in Sioux Falls, the system is not removing enough moisture from the air. This usually means the unit is oversized, the refrigerant is low, or the system is short cycling before it can do its dehumidification job. High indoor humidity makes the house feel warmer than it is and encourages mold growth. Call (605) 231-9370 to have the system evaluated before mold becomes a problem.
Telltale Signs
Warning Signs to Watch For
- The thermostat reads 72 but the house feels warm and clammy
- Windows fog up or show condensation on the inside during summer
- A musty smell develops in the basement or in rooms that are rarely opened
- Wood floors or doors swell and stick in summer more than they used to
- A humidity meter reads above 60 percent indoors with the AC running
Root Causes
What Causes High Humidity Inside With AC Running?
Oversized AC Unit Running Short Cycles
Dehumidification happens when warm humid air stays in contact with the cold coil long enough for moisture to condense out. An oversized unit cools the air so fast that it shuts off before that process happens. This is a frequent problem in homes on the west side of Sioux Falls where subdivisions built in the 2000s sometimes got systems sized for resale appeal rather than accurate load calculations.
The Fix
System Right-Sizing and Load Calculation
A technician runs a proper load calculation to determine the correct unit size. Replacing an oversized unit with the right size improves both comfort and humidity control significantly.
Low Refrigerant Level
When refrigerant is low, the coil temperature rises and the system loses its ability to condense moisture out of the air efficiently. The unit runs but humidity stays high because the coil never gets cold enough to do the job. This is common in Sioux Falls systems that are 8 to 15 years old and have developed small refrigerant leaks over time.
The Fix
Leak Detection and Refrigerant Recharge
A technician finds and fixes the leak, then recharges the system to the correct level. Once the coil runs at the right temperature again, humidity control improves noticeably within a day.
Self-Diagnosis
Which Cause Applies to You?
Check the signs you're observing to narrow down the likely root cause before your inspection.
| What You're Seeing | Oversized AC Unit Running Short Cycles | Low Refrigerant Level |
|---|---|---|
| Humidity is high but temperature at the thermostat is at the set point | ||
| System is not cooling as well as it did last summer | ||
| AC cycles on and off very frequently throughout the day | ||
| Ice forms on the refrigerant line during operation | ||
| Humidity problem started after a new unit was installed |
Free Inspection
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