Why your AC is not cooling, and what to check first

An AC that runs but does not cool is the most common call we get between May and September. A good share of them turn out to be something the resident could have sorted in ten minutes, which is worth knowing before you spend a day waiting in.

Here is what to check, in the order worth checking it.

1. The filter

Pull the front panel of the indoor unit open — it is designed to be opened — and look at the filter.

If it is grey and furred, that is very likely your whole problem. A blocked filter starves the unit of air, so it cannot move heat, and the symptom is exactly “running but not cooling”. In Dubai a filter in a lived-in flat can go from clean to choked in a couple of months.

Wash it in warm water, let it dry completely, and put it back. A damp filter refitted is how you get a smell next week.

2. The thermostat, properly

Not just the set temperature — the mode.

Cooling mode and fan mode look almost identical on most remotes, and fan mode moves air without cooling it at all. If the unit is blowing but the air is room temperature, check the mode icon before anything else. Check too that nothing has set it to a schedule or an energy-saving mode you did not intend.

3. The outdoor unit

If you have a split system with a condenser on a balcony or roof, go and look at it.

It should be running, and the air coming off it should be hot. If the fan is not turning at all while the indoor unit runs, that is a fault — stop here and call.

If it is running, check nothing is blocking it: stored boxes, a cover someone left on over winter, plants grown across the grille. A condenser needs clear air all round. In a Dubai summer, one that is boxed in will give up.

4. The drain and the drip tray

Look underneath the indoor unit. Water dripping, or a damp patch below it, means the condensate drain is blocking.

That matters for cooling as well as for your ceiling: many units have a float switch that shuts the system down when the tray fills. The symptom reads as “stopped working” when the cause is a blocked drain.

5. The breaker

If the unit is completely dead, look at the distribution board. A tripped breaker is either an overload or a fault.

Reset it once. If it trips again, stop. Repeatedly resetting a breaker is overriding a safety device, and the fault it is protecting you from has not gone anywhere. That is an electrical job.

Stop and call if you see any of these

• A burning smell, or scorching around a socket, isolator or the board. Switch it off at the breaker and call.
• The breaker trips every time the AC starts. Something is drawing fault current.
• Ice on the pipework or on the indoor coil. Usually low refrigerant or an airflow problem, and running it like that damages the compressor. Switch it off and let it defrost before anyone looks at it.

None of those are wait-and-see.

What it usually turns out to be

When none of the five checks solves it, the common causes in Dubai are:

• Low refrigerant from a leak. A sealed system should not lose gas. If yours is low, something is leaking, and a top-up alone just buys a season.
• A dirty evaporator coil. Behind the filter, and not something to tackle yourself. Cleaning it is a service job.
• A failed capacitor. Cheap, common, and it stops the compressor or fan starting. Often presents as a hum with no cooling.
• A fan or motor fault, usually preceded by weeks of a new noise nobody acted on.
• A failed thermostat or sensor, which makes the unit cycle on the wrong readings.
• In a tower, a building chilled-water problem — if neighbours have the same issue on the same day, it is the building, not your flat. Tell the building management before paying anyone.

That last one is worth checking first in an apartment. We have attended flats where the answer was a riser valve two floors down.

Before you book anyone

Write down what you have already checked. It saves a diagnosis step and it stops you paying someone to wash a filter you have already washed.

If you want it looked at properly, our AC maintenance and repair page sets out what a visit covers, or send us the job with a photo of the unit and the model label.

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If it is 45 degrees outside and the flat is climbing, call rather than filling in a form. A form is slower than a phone.