Why an ACstops cooling
The system is running and the house is getting warmer. These are the usual causes, from easiest to hardest to fix.
Seven causes
A clogged filter
A loaded filter chokes airflow. The house warms slowly and the coil may ice. Check and replace it. The Department of Energy advises monthly changes in the heaviest seasons.
The thermostat
Dead batteries, a wrong mode or a changed schedule can look like a failure. Set it to cool and a few degrees below room temperature.
A tripped breaker or disconnect
The outdoor unit has its own breaker and a disconnect box near the cabinet. If the breaker trips again right after a reset, stop resetting it.
A dirty outdoor coil
Leaves, cottony seed fluff and grass clippings keep heat from leaving the system. A gentle hose rinse with the power off can help.
A frozen indoor coil
Ice means airflow is restricted or the refrigerant charge is low. Turn the system off and let it thaw.
A failed capacitor or contactor
The outdoor fan or compressor will not start, or starts and stops. These parts sit behind panels that are not for homeowners to open.
Low refrigerant
Refrigerant does not get used up. If the charge is low there is a leak, and adding more without finding the leak only delays the next call.
Why it happens in the hottest week
Dallas/Fort Worth averages 9.7 days a year at 100 degrees or higher in August and 7.4 in July. The system runs near-continuously in those weeks, so a part that was marginal in June gives out.
That is also why tune-ups happen in spring. Catching a worn capacitor before July beats finding it when the house is 90 degrees inside.
When to stop and call
Call when the filter and thermostat are fine and the air is still warm, when there is ice you did not cause, when a breaker keeps tripping, or when you hear grinding or a loud buzz.
Do not open the cabinet panels or touch the refrigerant lines. Both involve electrical and pressure hazards.
Call and get a contractor on the line
The number connects you with an independent HVAC contractor that serves your ZIP code. Early in the day usually leaves more room on a contractor's schedule.