The air conditioner runs but does not cool: causes and a safe order of checks
The real reasons cooling is lost, from filters and drainage to outdoor-unit placement and the refrigerant circuit, and which steps belong to a technician.
Start with filters and airflow
Most complaints about weak cooling are about the volume of air moving through the unit rather than the unit itself. A blocked filter starves the coil, the coil then runs too cold and ices over, and the result is a machine that blows without cooling. Switch the unit off before removing the filters and, where possible, isolate its breaker; wash the filters in lukewarm water and refit them only when they are completely dry, out of direct sun. Fitting a damp filter is a direct invitation to odours and mould. If airflow is still weak with clean filters, the coil or the fan may be fouled, and at that point asking for a service is better than opening the indoor casing yourself.
The outdoor unit and where the heat goes
An air conditioner does not create cold; it moves heat from inside to outside. If the outdoor unit cannot release that heat, the room will not cool however long the machine runs. There must be clear air space in front of and behind the unit, and the fins must not be packed with dust, leaves or nesting material. A unit tucked into an enclosed balcony recess or a narrow light well re-inhales its own hot discharge and loses efficiency quickly, and there the first fix is the position, not the machine. Never cover the outdoor unit or store things on top of it, and never work on the fins without first cutting the power.
Settings, use and the load on the room
A share of service calls turn out to be settings rather than faults. Confirm the unit is in cooling mode and has not been left on dry or fan only; if the setpoint sits very close to room temperature the compressor cycles off quickly and cooling is barely felt. Weak batteries in the remote can also mean commands never fully reach the unit. In south- and west-facing rooms, closing blinds during the day, shutting the door between kitchen and living room and keeping the balcony door properly sealed noticeably reduces the load. A unit whose capacity was chosen too small for the room will never reach the setpoint; that is a selection error rather than a fault, and only the right capacity resolves it.
Drainage, icing and dripping water
Water from the indoor unit almost always means the condensate formed during cooling cannot drain away. A blocked, kinked or badly sloped condensate hose lets the tray fill until it overflows out of the casing. If you can see ice on the coil, switch the unit off and let it thaw naturally; chipping at the ice or pouring hot water over it damages the fins. Icing points to one of two things: airflow is too low, or refrigerant pressure is too low. The second means the system is leaking, and simply adding gas does nothing but postpone the same fault.
Work that belongs to a technician
The refrigerant circuit is a sealed system under pressure; pressure checks, leak detection, brazing and evacuation require proper equipment and competence and cannot be done with household tools. Opening the electrical box of either unit, replacing boards or capacitors and retightening terminals is likewise technician work, since capacitors can hold a charge even with the unit switched off. If the unit trips its breaker while running, smells of burning or its casing becomes hot, stop using it and switch off the supply breaker. On the heating side, nothing connected to a boiler, water heater or natural gas line should be touched; that work belongs to a licensed service only.
