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AC Running but High Humidity Indoors
in Plano, TX
Removing humidity is just as important as lowering the temperature. Plano sits in a region where summer mornings can bring outdoor humidity above 80 percent, and that moisture finds its way into homes through gaps in the building envelope. If your AC can't keep indoor humidity below about 50 percent, mold starts to grow in as little as 48 hours on surfaces you may not even see.
Quick Answer
High indoor humidity with the AC running usually means the system isn't removing moisture the way it should. In Plano, where outdoor humidity regularly hits 70 to 80 percent during summer mornings, an oversized or short-cycling AC never runs long enough to wring moisture out of the air. Call (469) 960-3779 to find out if a system issue or an infiltration problem is driving the humidity.
Telltale Signs
Warning Signs to Watch For
- Indoor humidity gauge reads above 55 percent regularly
- Condensation on windows or cold surfaces even with the AC running
- A damp or musty smell that doesn't go away
- Wood floors or doors swelling or sticking
- Allergy symptoms worse than usual inside the home
Root Causes
What Causes AC Running but High Humidity Indoors?
Oversized System Not Running Long Enough
A unit that's too large cools the air temperature quickly and shuts off before it has time to pull moisture out of the air. Dehumidification happens over the course of a longer run cycle. Many Plano homes that got new, larger systems installed between 2010 and 2020 ended up with units that cool fast but leave the air feeling damp all summer.
The Fix
Load Calculation Review and Dehumidification Strategy
A technician assesses whether the system is properly sized and discusses options, which may include a whole-home dehumidifier added to the existing system or a properly sized replacement unit.
Air Infiltration Through the Envelope
Outdoor humid air gets into homes through gaps around windows, doors, recessed lights, and attic hatches. When outdoor air in Plano reaches 80 percent humidity on a June morning and seeps steadily into your home, the AC has to work constantly to remove it. Homes built before 1990 in older Plano neighborhoods near Spring Creek Parkway often have gaps that were never properly sealed.
The Fix
Air Sealing and Infiltration Inspection
A technician or energy auditor locates infiltration points using a blower door test and seals gaps with appropriate materials. Reducing the amount of outdoor air getting in takes pressure off the AC system and makes humidity control much easier.
Dirty Evaporator Coil Reducing Moisture Removal
A clean evaporator coil is cold enough to cause moisture in the air to condense on its surface and drain away. When the coil is coated in dust, its surface temperature rises and it removes less moisture with each pass of air. In Plano where the system runs from April through October, coils that aren't cleaned annually lose their dehumidification efficiency before the worst of summer arrives.
The Fix
Evaporator Coil Cleaning
A technician cleans the coil surface, checks the drain pan, and clears the drain line so removed moisture exits the home properly. Annual coil cleaning in the spring keeps the system removing humidity at full capacity through the summer.
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 System Not Running Long Enough | Air Infiltration Through the Envelope | Dirty Evaporator Coil Reducing Moisture Removal |
|---|---|---|---|
| AC cools the house to set point quickly but humidity stays high | |||
| Humidity is highest in rooms near exterior walls or the attic hatch | |||
| Coil is visibly dusty or has not been cleaned in over a year | |||
| System was recently upgraded to a larger unit | |||
| Humidity rises fastest in the morning when outdoor humidity is high | |||
| Drain line is dripping very little even though AC runs all day |
Free Inspection
Get a Diagnosis in Plano
An on-site inspection is the only way to confirm which cause applies to your property. Free, no obligation.
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Serving Plano & surrounding areas
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