Start with the controls and airflow
Confirm that the controller is set to cooling rather than fan, dry or heating mode, and select a temperature below the current room temperature. Close external doors and windows, allow the system time to respond and check that the indoor airflow is not blocked by furniture or curtains.
If the manufacturer instructions allow homeowner filter cleaning, inspect the filters and follow those instructions exactly. Restricted filters can reduce airflow, but a filter clean will not correct every fault. Do not remove fixed covers or reach into the unit.
What may need professional investigation
Low airflow, dirty heat-exchange surfaces, sensor faults, outdoor-unit problems and electrical or control issues can all reduce performance. Refrigerant loss is another possibility, but it must be investigated rather than treated as a routine top-up.
A technician can compare temperatures, airflow and operating behaviour with the equipment data, inspect drainage and electrical condition, and test the refrigeration circuit where appropriate. That evidence is more useful than replacing parts by guesswork.
When to stop using the system
Switch the affected unit off and seek help if there is a burning smell, unusual electrical noise, repeated tripping, water close to electrical parts or signs of damage. Use the normal controller or local isolator only when it is safe to do so.
For persistent poor cooling across Kent, Top Local can arrange practical fault finding. Share the model, what the unit is doing, when the problem started and any displayed code when you call.