An AC that never seems to shut off, yet fails to bring the room down to the set temperature, points to the system struggling against a load it can't keep up with rather than a simple malfunction. A refrigerant leak reduces the unit's actual cooling capacity below its rated output, so it keeps running in an attempt to reach a target it's no longer capable of hitting.
A severely dirty condenser or evaporator coil creates the same effect by limiting how efficiently heat can be absorbed indoors and released outdoors, even though every component is technically functioning. In some cases the room itself has changed, such as added heat-generating equipment, additional occupants, or increased sun exposure from nearby construction removing shade, pushing the actual heat load beyond what the originally sized unit was intended to handle.
A failing capacitor can also cause the compressor to run inefficiently without fully failing, drawing more power while delivering less cooling. Because continuous running without effect wastes significant electricity while accelerating component wear, this symptom generally warrants a diagnostic visit rather than simply lowering the thermostat further.