Start with the thermostat
It sounds too simple, but thermostat settings cause a surprising share of no-cooling calls. Confirm the thermostat is set to cool, not just fan. In fan-only mode the blower circulates room-temperature air all day and the house never gets cooler, which feels exactly like a broken AC.
Check that the set temperature is actually below the current room temperature, and if your thermostat runs on batteries, replace them. A dying thermostat can display normally while failing to signal the outdoor unit to start.
If you recently had a power outage, which is not rare during Charleston summer storms, some thermostats and outdoor units need a few minutes to reset. Give the system five to ten minutes after restoring power before deciding something is wrong.
Check the filter and the airflow path
A severely clogged filter can make cold air feel weak and warm by the time it reaches your rooms, because so little air is moving that it picks up heat on the way. Pull the filter and hold it up to a light. If you cannot see light through it, replace it.
Walk the house and confirm supply vents are open and return grilles are not blocked. In older Charleston homes with ductwork in hot attics or vented crawl spaces, a disconnected or torn duct can dump your cold air into the attic while the rooms stay warm. Weak airflow from one area of the house while other rooms are fine often points to a duct problem rather than an equipment problem.
Duct leakage is worth taking seriously here because attic temperatures in a Lowcountry summer are brutal. Air traveling through leaky attic ducts absorbs heat fast, so even a healthy system can deliver disappointing air to the far rooms of the house.
Look at the outdoor unit
Your outdoor condenser is where the heat collected from inside your home gets released. If it cannot shed that heat, the whole system loses capacity. Go outside and look at it while the system runs. The fan on top should be spinning and you should feel warm air blowing out.
Clear away anything crowding the unit. Grass clippings, oak pollen, palmetto fronds, leaves, and shrubs planted too close all block the coil. The unit needs generous clearance on all sides to breathe. If the coil fins look caked with dirt or lawn debris, gently rinsing them with a garden hose, with the power off at the disconnect, can restore real capacity.
If the outdoor fan is not spinning, or the unit hums but does not start, or it is completely silent while the indoor blower runs, stop there. Those symptoms point to a failed capacitor, contactor, or fan motor, all of which are professional repairs involving high-voltage components.
- Fan spinning and warm air blowing out means the condenser is at least trying
- A loud hum with no fan movement often means a failed capacitor
- Ice on the copper lines means shut the system off and let it thaw
- Keep shrubs and fencing well clear of the unit on every side
Refrigerant problems
If the system runs, airflow is decent, and the outdoor unit looks healthy, but the air from the vents is barely cool, low refrigerant is a prime suspect. A system low on refrigerant cannot absorb much heat, so it runs continuously while the house temperature creeps up through the afternoon.
Low refrigerant means a leak somewhere in the circuit. Coastal corrosion, vibration wear on copper lines, and factory joint failures are common sources. The correct fix is leak detection and repair followed by an accurate recharge, not a seasonal top-off that leaks out again.
Refrigerant work requires EPA certification and proper gauges, so this is where troubleshooting hands off to a technician. Be wary of anyone who quotes adding refrigerant without discussing where it went.
When the system is simply outmatched
Sometimes nothing is broken. During a Charleston heat wave, with heat indexes soaring and humidity near saturation, a correctly sized air conditioner may run almost continuously during the hottest hours and hold the house only moderately cooler than outside. Long run times in extreme weather are normal and actually good for dehumidification.
The concerning pattern is a house that used to keep up and no longer does under similar weather. That drift usually means lost capacity from a dirty coil, a refrigerant leak, duct degradation, or an aging compressor, and it deserves a diagnostic before peak season.
If your system is more than a decade old and losing ground every summer, it is worth weighing repair against replacement rather than paying to chase capacity year after year. Our team can measure what the system is actually delivering and give you an honest read.
