Why your AC runs all day in August and still cannot keep up

The house holds 78 during the day, creeps to 80 by late afternoon, and the outdoor unit has not stopped since noon. The first thought is that the AC is undersized or dying. Usually it is neither. The system is losing the cold it makes before the cold reaches the rooms.

Where the cold goes

• Attic ductwork. In a 140-degree attic, a duct run with a torn section or a disconnected boot is cooling the attic. We find at least one leak in most attics we enter.
• Dirty evaporator coil. A coil coated in dust cannot transfer heat, so the system runs longer to do the same job. It also runs colder and wetter, which is the musty smell story.
• Thin insulation. Heat comes through the ceiling faster than the system can remove it. See our attic insulation post.
• Leaking return plenum. The return pulls hot attic air into the system, and the AC spends its capacity cooling air that was never in the house.
• Dirty blower wheel and restricted filter. Less air moves, so less cooling is delivered, even if the unit is producing it.

What to check before calling for a new unit

Filter first. Then go into the attic with a flashlight and look at the duct runs: crushed flex, disconnected joints, insulation sagging off the trunk. Look at the insulation depth. If any of that looks wrong, the unit is not the problem yet.

What we do on the inspection

We open the air handler and photograph the coil and blower, walk the attic and photograph every duct connection, measure insulation depth, and check the plenums. You get a written list ordered by what matters most and what it costs. In a lot of Georgetown and Leander homes the answer is a sealed return, a clean coil and a few duct repairs, and the unit stays.

When it really is the unit

Refrigerant issues, a failing compressor or a system that is 15 years old with a history of repairs. We do that work too, and we will tell you when repair versus replace tips over. But we check the ducts first, because a new unit on bad ducts has the same problem next August.