Does this match your problem?
- AC runs but blows warm or room-temperature air
- Outdoor unit is silent while thermostat calls for cooling
- Ice buildup on the copper line or indoor coil
- House never reaches the set temperature
Quick check first
Set the thermostat to COOL, drop the target 5°F below room temp, and confirm the fan is set to AUTO (not ON). If nothing kicks on within 2 minutes, keep going.
Step-by-step troubleshooting
1. Check the thermostat mode and batteries
Confirm the thermostat is in COOL mode, batteries are fresh (if applicable), and the set temperature is at least 3°F below the current reading. A dead thermostat is one of the most common no-cool calls.
2. Inspect the air filter
Pull the filter and hold it up to a light. If little or no light passes through, it's dark gray, or it bows in the middle, you've likely found your problem: a starved filter chokes airflow across the evaporator coil, which drops cooling capacity and can freeze the system solid. In Raleigh's pollen season a 1-inch filter can load up in 30 days. Filter grades, sizing, and the right replacement routine are covered step by step in the DIY Quick-Fix Playbook, or any of our techs can handle it during a visit.
3. Reset the breakers
Find the two AC breakers in your main panel, one for the outdoor condenser, one for the indoor air handler. Flip both fully OFF, wait 60 seconds, then flip fully ON. Also check the outdoor shutoff box next to the condenser.
Warning: If a breaker immediately trips again, stop. A repeat trip means a short or seized component, call a licensed pro before you damage the compressor.
4. Look for ice on the copper line
Go to the outdoor unit and check the larger insulated copper pipe. If it's frosted or iced up, turn the system OFF at the thermostat and run the fan ONLY for 2–3 hours to thaw. Icing is caused by low airflow (dirty filter) or low refrigerant (needs a pro).
5. Inspect the outdoor condenser
Walk out to the unit and look, don't touch. Is the coil matted with cottonwood fuzz, grass clippings, or dirt? Are shrubs, fencing, or mulch crowding within 24 inches? A condenser rejects your home's heat through those fins; when it can't breathe, cooling capacity drops hard and the compressor runs hot. If the coil looks matted or the unit is boxed in, you've found a likely cause. Safe coil cleaning is covered in the Playbook, done wrong, fin damage and water in the electricals turn a cheap problem into an expensive one.
6. Check the condensate drain
Many systems have a float switch that shuts the AC off when the condensate line clogs. Look for standing water in the drain pan under the indoor unit, and pull the cap on the vertical access tee (the open PVC stub near the unit) to look for a visible clog in the trap. Outside, find the drain's exit stub, on a humid day with the AC running it should drip; a dry stub points to a blockage. If you see standing water or no drip, you've found it. Clearing the line properly is in the Playbook, or we can handle it during a visit.
7. Compare supply and return temperatures
With the AC running normally, hold a thermometer at a supply vent and a return vent. You want a 14–20°F temperature drop from return to supply. Less than 14°F points to low refrigerant, a failing compressor, or a metering issue, all pro repairs.
Stop and call a licensed pro if:
- •Breakers trip repeatedly after you reset them
- •You smell burning, hear grinding, or see sparks
- •The refrigerant line iced up with a clean filter installed
- •Supply-to-return temperature split is under 14°F after a filter change
- •Outdoor unit hums but the fan does not spin (bad capacitor or motor)
- •The system is over 10 years old and cooling has been declining for months