AC is running but not cooling
20 minutes · Easy · Estimated materials $0–$35
Start with airflow, thermostat and outdoor-unit checks before assuming the system needs refrigerant.
Likely cause
A clogged filter, incorrect thermostat setting, blocked outdoor coil or a tripped disconnect is more common than a failed compressor.
First safe check
Set the thermostat to Cool, lower it five degrees, and confirm air is moving from a supply vent.
Tools and materials
Tools
- Flashlight
- Clean replacement filter
- Work gloves
Materials
- Correct-size HVAC filter
Step by step
- 1Confirm the thermostat is on Cool and the fan is on Auto.
- 2Check the return filter; replace it if gray, bowed or difficult to see through.
- 3Check that supply and return vents are open and unobstructed.
- 4From the ground, look for leaves or debris blocking the outdoor unit; keep two feet clear.
- 5Check the labeled HVAC breaker once. If it trips again, leave it off.
Common mistakes
- Buying refrigerant before checking airflow
- Resetting a breaker repeatedly
- Running a frozen system
When to call a professional
Heating and cooling
Most of this is yours to do. Call someone licensed if any one of these is true — it's a judgement call, not a defeat.
- The fix would involve refrigerant of any kind.
- The unit trips its own breaker or short-cycles.
- You see ice on the lines in normal weather.
- Airflow is fine but the system still won't hold temperature.
General guidance only. Codes and conditions vary. When in doubt, stop and use a licensed professional.