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That musty, gym-bag smell when the AC first kicks on has a specific cause: biofilm. Fine dust that gets past the filter lands on a coil and drain pan that stay wet for six months of the year, and the mixture grows mould and bacteria. The smell is the mildest symptom — black dust streaks around supply vents and indoor allergy flare-ups point the same way, and in a country where people live sealed indoors from May to October, indoor air quality is not a luxury concern.

Duct cleaning and coil cleaning are different jobs; know which you are buying. A chemical coil wash treats the wet heart of the unit — evaporator, blower wheel, drain pan — and fixes most smells; it earns its keep annually. Duct cleaning treats the tunnels: proper firms use rotating brushes or air whips to agitate dust and a negative-pressure vacuum to extract it, section by section. A man with a household vacuum and a torch is redistributing your ducts' contents, not cleaning them. Honest frequency is boring: every two to three years, sooner after renovation (gypsum dust is ductwork's worst enemy) or when moving into a flat with unknown history. Anyone insisting every home needs it every six months is selling frequency, not hygiene.

In August humidity a hard-working unit pulls several litres of water a day out of your air. All of it lands in a shallow pan under the coil and leaves through a narrow drain pipe that runs nearly flat above your ceiling, stays damp all year, and is fed a steady diet of fine dust — perfect conditions for algae and sludge. When it blocks, the pan overflows quietly into the ceiling void, and the first sign is a spreading brown stain or a drip through a light fitting. In apartments there is a twist: the stain on your ceiling is very often the upstairs neighbour's FCU, because drain trays sit in the slab void between floors. Establish whose unit is leaking before paying for repairs.

The fix is undramatic: flush and vacuum the drain line, clean the pan, check the pipe's slope, and drop in a slow-dissolving anti-algae tablet. It is a standard line in a proper service, and at AED 150–300 as a standalone job it is cheap insurance against repainting a ceiling. If a unit has overflowed once, ask about fitting a float switch — a small sensor that shuts the unit down before the pan overflows again.

You can judge a service visit by its sequence. A thorough technician starts with the story (what changed, when), then measures before touching anything: air temperature entering the return and leaving the supply. On a healthy DX system that split is roughly 8–12°C; a smaller gap points to low refrigerant or dirty coils, a bigger one with weak flow points to airflow restriction. It is a thirty-second test that converts a vague complaint into a number. Then the electrical checks: compressor amp draw against its nameplate figure, and the run capacitor's actual microfarads against its rating. Heat kills capacitors, making them the most commonly failed electrical part in UAE condensers — a AED 200–450 swap has rescued many units declared dead. On DX systems, gauges go on the service ports; on FCUs the checks shift to valve actuation, water flow and motor bearings.

Then the wet work: filter and coil condition, blower wheel, drain pan and line flushed and confirmed flowing, condenser fins washed from the inside out so dirt exits the way it came. A visit that skips the measurements and goes straight to hosing the filter is cleaning, not maintenance. Ask for the numbers — temperature split, amps, pressures — on the job report; a technician confident in the work will write them down, and the report becomes your baseline for next time.