Short answer: When an AC runs but doesn't cool, the most common causes are clogged filters and coils, an outdoor unit that isn't running (often a failed capacitor or outdoor fan), a refrigerant leak, or a sensor or board fault. Start by cleaning the filters, checking the mode is set to Cool, and looking at whether the outdoor fan is spinning.
Quick Checks You Can Do
- Mode and temperature: set to Cool (not Fan or Dry) and a temperature below the room's.
- Filters: lift the front panel, slide out the filters, rinse, dry and refit. Clogged filters alone can halve cooling.
- Outdoor unit: is the fan spinning and the unit humming? Is it blocked by boxes, plants or a cover?
- Doors and windows: a big room with open doors or direct afternoon sun overwhelms any AC.
Faults That Need a Technician
- Outdoor unit silent or humming without starting: capacitor, contactor or board
- Ice on the pipes: low gas from a leak, or very dirty coils
- Weak cooling despite clean filters: dirty evaporator or condenser coils need a jet service
- Cools, then stops after a while: outdoor unit overheating, a failing fan, or a sensor fault
- Error code or blinking light: sensor, fan or inverter board
Is it always a gas problem?
No. Dirty coils and a weak capacitor are more common than leaks. And if gas is low, there's a leak to fix. Gas refill vs leak repair
