The AC runs all afternoon and the house never cools

Why it shows up in the afternoon

A Bastrop August averages a 97°F high at the nearby Smithville station. An AC that is a little short on charge or airflow keeps up at 9 a.m., falls behind by 2 p.m. and is several degrees off the setting by 5. The same system can seem fine in the morning and fail the household every afternoon.

A system that cools a little has not stopped working. It is working at a fraction of its capacity, and running nonstop is how it shows. Long run times also leave the house clammy, because the coil never gets cold enough to pull much water out.

What a technician measures

The temperature split. The difference between the air going into the return and the air coming out of a supply vent. A split well under normal points at refrigerant or a dirty coil; a normal split with weak air at the vents points at airflow.

Pressures at the outdoor unit. Gauges on the service valves show whether the charge is low. A low charge means a leak, and the visit should include a leak search, not only a top-up.

The coils. The outdoor coil packed with cottonwood fluff, grass clippings or pine pollen cannot shed heat. The indoor coil, in the attic or a closet, can be matted with dust when filters were skipped.

What you can check before calling

• The filter. A clogged one can cut airflow enough to cause exactly this.
• The outdoor unit: both the fan and the compressor running, nothing stacked against the coil.
• Supply vents and the return grille open and unblocked.

Then stop. Hosing the coil hard, opening panels or adding refrigerant is the technician's work.

What to say when you call

• That it runs constantly and does not reach the setting, and from what time of day
• The thermostat setting and the reading at the worst point of the afternoon
• The install year and the refrigerant on the outdoor data plate
• Whether it has been topped up with refrigerant before
• Your ZIP code, and where the indoor unit sits

Common questions

Is the AC simply too small for the heat? Possible on a house that has been added to, but a system that used to keep up and no longer does has usually lost something it had.

Will it get better at night? It usually catches up after dark, which is why the fault gets put off. The leak or the dirty coil is still there the next afternoon.