One Room Warm, Other Rooms Fine: Coil Buildup, Not Low Gas

One bedroom in a flat failing to hold temperature while the other rooms cool well and consistently. Air from the affected unit feels cool but sparse. The household has already been told the system needs gas.

The distribution of the complaint eliminates the most commonly quoted cause before anything is measured. A charge shortfall reduces cooling everywhere it reaches, so rooms performing normally are themselves evidence that the charge is adequate. That redirects the whole visit onto the single unit that is failing, and specifically onto whether it is moving enough air across its own coil to make a difference to the room it serves.

Where several indoor units share one outdoor unit and one charge, anything shared shows itself in every room. A single indoor unit falls behind only when something belongs to that unit alone. In practice that means its own filter, its own blower or its own coil. Deposit across a coil face reduces airflow and heat transfer at the same time, so the air comes out cool and there is far too little of it to change the room.

The affected coil is cleaned and the room recovers, with the charge left untouched because there was never anything wrong with it. The reasoning generalises much further than the repair does. Before agreeing to a top-up on any system, ask what pattern would be expected if the charge really were low, then check whether the symptoms in front of you actually match it.