AC turns on and off every few minutes? House humid with the air running?

What short cycling is

An air conditioner is meant to run for a stretch — long enough to pull the room down to the thermostat setting and, just as important, long enough to pull moisture out of the air. When a system starts, runs a few minutes, stops, and starts again a few minutes later, that pattern is called short cycling. It is a symptom, not a diagnosis, and it has several common causes.

Why the house feels humid even though it is cold

Cooling and drying happen on the same coil, but drying is the slower of the two. Moisture condenses out of the air only while the coil is cold and air is moving across it. A system that satisfies the thermostat in a few minutes never runs long enough to wring the air out, so the house reads 72 degrees and feels clammy. In San Antonio's humid summers that second job is most of the comfort.

The causes people expect — and the one they do not

1. A dirty filter or blocked airflow. Starved of air, the coil can ice up and the system trips off. Check the filter first; it is free.
2. A thermostat in the wrong place. A thermostat in direct sun, over a lamp, or beside a supply vent reads the wrong room.
3. Low refrigerant or a failing part. These need a technician with gauges; a system that is low did not get that way on its own.
4. A system that is too big for the house. This is the one people do not expect. A unit sized by a square-footage rule of thumb often comes out larger than the house needs. It cools the air in minutes, shuts off before it has dried anything, and repeats — more starts, more wear, a clammier house, and a higher bill than a right-sized system would run.

Bigger is not safer

The instinct to "go up a size to be safe" works against you in a humid climate. The right size comes from the house itself — its windows and their facing, the attic insulation, the ducts, the number of people who live there — worked through a load calculation. That is not a sales line; in San Antonio it is the code.

What to do

1. Change the filter and make sure supply vents and the return are open and clear.
2. Check where the thermostat sits and what is near it.
3. If it still cycles, have a technician check refrigerant and controls.
4. If anyone proposes a replacement, ask for the load calculation before you sign — from us or from anyone else. A quote that names only a tonnage and a price has skipped the step the code requires.

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