1. Check the thermostat
Make sure it is set to Cool, not Fan or Heat, and set a few degrees below the room temperature. If it runs on batteries, replace them. A blank or flickering screen can stop the system from calling for cooling.
2. Replace a dirty air filter
A clogged filter chokes airflow, which can make the indoor coil freeze and stop cooling. In North Texas summers, check filters monthly and replace them every one to three months.
3. Look for ice
Ice on the copper line going into the outdoor unit or on the indoor coil means the system is freezing up. Turn the AC off and run just the fan for a few hours to thaw it. If it freezes again after you replace the filter, call a pro, because low refrigerant or a blower problem is likely.
4. Check the outdoor unit
Go outside while the AC is on. If the fan on top is not spinning or you hear a hum with no fan, the capacitor may have failed. This is one of the most common AC repairs in Texas heat. Capacitors hold a dangerous charge, so do not touch it yourself.
- Clear leaves, grass and debris at least two feet around the unit.
- Check the breaker in your electrical panel and the shutoff box next to the unit.
- Gently rinse a dusty outdoor coil with a garden hose, with the power off.
5. Consider the heat
On 100°F-plus days, many systems cannot hold the house far below the outdoor temperature. A healthy system can still struggle in extreme heat. If the air from your vents is cool but the house is slowly warming in the late afternoon, that may be normal for your system size.