Before calling, confirm the thermostat is set to Cool and below room temperature, check both HVAC breakers and the outdoor disconnect, replace a dirty filter, and see whether a clogged condensate drain has tripped a float switch. If lines are iced, turn cooling off to thaw. Refrigerant, electrical, and compressor problems need a licensed technician.
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When the AC quits on a 95-degree Atlanta afternoon, it's natural to want someone out right away. A few safe checks can sometimes get the system running again, or at least help you describe the problem clearly when you call. None of the steps below involve opening electrical panels or handling refrigerant. Leave that to a licensed technician.
1. Check the thermostat
- Make sure it's set to Cool, not Heat, Off, or Fan only.
- Set the temperature a few degrees below the current room temperature.
- If the screen is blank or dim, replace the batteries. Some thermostats run on batteries even when wired to the system.
- If you have a smart thermostat, check the app for schedules, eco modes, or an alert that it has lost power from the system.
2. Check the breakers and the outdoor disconnect
A typical split system has two parts on separate circuits: the indoor unit (a furnace or air handler) and the outdoor condenser or heat pump. Look in your electrical panel for both breakers. If one has tripped, reset it once. If it trips again, stop and call for service, because repeated tripping points to an electrical or compressor problem.
Next to the outdoor unit there's usually a disconnect box. Make sure it hasn't been pulled or switched off, which sometimes happens after yard work or a previous service visit. The indoor unit usually has a switch that looks like a light switch on or near the equipment. Confirm it's on.
3. Replace a dirty filter
A clogged filter is one of the most common reasons for weak airflow and poor cooling. It can also cause the indoor coil to freeze. Pull the filter and hold it up to a light. If you can't see through it, replace it. During Atlanta's spring pollen season and heavy summer use, filters can load up faster than the label suggests. Also make sure return grilles and supply registers aren't blocked by furniture or rugs.
4. Look for ice
Ice on the copper refrigerant lines at the outdoor unit, or frost on the indoor coil, usually means low airflow or low refrigerant. Running the system frozen can damage the compressor. Set the thermostat to Off, or run only the fan, and give it several hours to thaw completely. Put in a clean filter. If it ices up again after restarting, the system needs a technician. Low refrigerant means there's a leak somewhere; simply adding refrigerant without finding the leak is a short-term fix.
5. Check the condensate drain
An AC removes a lot of moisture from the air in a humid Atlanta summer, and that water drains through a condensate line. Many systems, especially those in attics, have a float switch that shuts the system off if the drain backs up, to prevent water damage. Signs include:
- Water in the secondary drain pan under an attic unit, or water dripping from a pipe over a window or eave.
- Standing water around the indoor unit in a basement or closet.
- The thermostat is calling for cooling but nothing runs at all.
Some homeowners clear the line at the cleanout with a wet/dry vacuum from the outdoor end. If you're not comfortable doing that, or there's water near electrical parts, call for service. Algae buildup in these lines is common in our climate, which is one reason a yearly tune-up includes flushing the drain.
6. Look and listen at the outdoor unit
With the thermostat calling for cooling, go outside and check:
- Is the fan on top spinning? If the unit hums but the fan doesn't turn, or nothing runs at all while the indoor blower is working, a failed capacitor or contactor is a frequent cause. These are electrical parts that store a charge, so don't poke at them; a technician can test and replace them.
- Are the fins clogged? Grass clippings, leaves, cottonwood, and pollen can coat the coil and keep the unit from shedding heat. With power off at the disconnect, you can gently rinse the fins from the inside out or top down with a garden hose. Don't use a pressure washer.
- Is there clearance? Keep shrubs, fences, and stored items a couple of feet away so the unit can breathe.
7. Know what's normal on extreme days
Residential systems are typically sized for a design outdoor temperature in the low to mid 90s for the Atlanta area, not for the hottest afternoon on record. On a very hot day, it's normal for a properly working system to run almost constantly and for the house to drift a few degrees above the setpoint by late afternoon. A rough check many technicians use is the temperature difference between air going into the return and air coming out of a nearby supply register. A difference somewhere around 15 to 20 degrees is often considered normal, though it varies with humidity and equipment. Much less than that suggests a problem.
Closing blinds on sun-facing windows, avoiding oven use in the afternoon, and setting the thermostat back to a reasonable temperature instead of dropping it very low can help the system keep up.
When to stop and call a professional
- A breaker trips more than once.
- You smell burning, see smoke, or hear grinding, screeching, or loud buzzing.
- The system ices up again after thawing.
- The outdoor unit hums but won't start, or nothing outside runs.
- There's water leaking near electrical parts or through a ceiling.
- Someone in the home is elderly, very young, or has a medical condition that makes heat dangerous. In that case, don't wait. Move to a cooler place if you need to.
What to tell the technician
You'll get a faster, more accurate diagnosis if you can share:
- The age and brand of the system, if you know it. The data plate on the outdoor unit usually shows a model and serial number.
- What you've already checked, and what you saw: ice, water, a tripped breaker, a fan that won't spin.
- Whether the problem came on suddenly or the system has been struggling for a while.
- Any recent work, such as a new thermostat, electrical work, or a past refrigerant recharge.
Ask for the diagnosis and a written price before repair work starts. If the system is older and the repair is major, such as a compressor or indoor coil, it's reasonable to ask for a replacement estimate too, so you can compare. In Georgia, HVAC work should be done by a licensed Conditioned Air Contractor; you can check a license on the Georgia Secretary of State's verification site.
If you've worked through these checks and the house is still warm, request help from a licensed HVAC contractor near you.
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Frequently asked questions
Why is my AC running but the house won't cool down?
Common causes include a dirty filter, a frozen indoor coil, low refrigerant from a leak, a dirty outdoor coil, or an outdoor unit that isn't running because of a failed capacitor or contactor. Check the filter and breakers first, then call a technician.
How long should I let a frozen AC thaw?
Often several hours, and sometimes most of a day for heavy ice. Turn cooling off, run only the fan if you want to speed it up, replace the filter, and have the system checked if it freezes again.
Is it normal for my AC to run all day in summer?
On very hot, humid Atlanta days, a properly sized system may run almost continuously and still fall a few degrees behind the setpoint by late afternoon. If it can't keep up on milder days, or the air from the vents feels barely cool, have it checked.