Air Conditioner Not Cooling? What to Check Before You Ring Anyone

It is running. You can hear it. The room is still warm. Every October the phone fills up with exactly this, and a fair share of them are things you can sort yourself in ten minutes. Here are the five worth checking before you ring anyone, in order, and the point where it stops being a you job.

First, what “not cooling” usually is

An air conditioner does two things: it moves air, and it pulls heat out of that air. When a unit stops cooling, nine times out of ten one of those two has fallen over. Either the air is not moving properly through the machine, or the machine cannot get rid of the heat it is collecting.

Up here it is overwhelmingly the first one. A Darwin unit runs eight months a year in humid air, and everything it breathes through — filters, coil, barrel fan, outdoor fins — clogs up faster than anywhere else in the country. Most of the checks below are about airflow for that reason.

1. The remote

Not a joke. We turn up to a surprising number of these. Check three things:

• Mode. The snowflake, not the sun, the fan, or the water drop. Dry mode and fan mode both blow air that is not properly cold, and it is easy to knock the button with a thumb.
• Temperature. Set it to 24 or lower and see if the air changes. If someone set it to 28 on a cool night in July, it will run all day and never feel cold.
• Timer or sleep mode. Both throttle the unit back. If there is a little clock or moon on the screen, clear it.

Hold your hand in front of the indoor unit. If the air coming out is clearly colder than the room, the machine is cooling. The problem is somewhere else — read on. If it is room temperature or barely cooler, keep going too.

2. The filters

Lift the front cover of the indoor unit. The two mesh panels are the filters. If you cannot see light through them, that is your problem, or a good part of it. A choked filter can halve the airflow and the unit will run flat out and get nowhere.

Slide them out, rinse them under the tap, let them dry completely, put them back. Wet filters grow mould in about a day up here, so dry means dry. Then run the unit for twenty minutes and see what changes.

While the cover is up, look past where the filters sit at the metal fins behind them and the plastic vanes at the bottom. If they are grey, furry or black-speckled, the coil and barrel fan are dirty, and that is not something a hose fixes. Put that on the list for the call.

3. The outdoor unit

The box outside is where the heat leaves. If it cannot breathe, nothing inside works. Go and look at it while the system is running.

• Is the fan spinning? It should be, and the air coming off it should feel warm. If it is humming and the fan is not turning, turn the system off and ring. That is a part, not a clean.
• Is anything in front of it? Plants grown up, a bin pushed against it, a sheet of tin leaning on it. It needs clear space around it. Move whatever is there.
• Are the fins blocked? The thin metal fins on the back and sides pack up with dust, leaves, grass clippings and dog hair. If you can see a mat of it, brush it off gently with a soft brush or rinse it with a hose on low pressure, away from the electrics. Do not pressure wash it — you will flatten the fins and make it worse.
• Is it in full afternoon sun? It will still work, but it works harder. Not a fault, just worth knowing when the afternoon is the only time it struggles.

4. Ice

Look at the copper pipes where they come out of the indoor unit, and at the pipes and valves on the outdoor unit. If any of it is iced up, you have found it. Ice means the coil has got too cold, and that happens for two reasons: not enough air going over it, or not enough refrigerant in it.

Turn the system off and let it thaw — a couple of hours, longer in a cold room. If the filters were filthy and you have just cleaned them, there is a reasonable chance that was the cause. Run it again and watch. If it ices up again with clean filters and a clear outdoor unit, it is refrigerant, and that is a licence job. More on that below.

5. Water where it should not be

Water dripping from the indoor unit, a wet patch on the wall under it, or spitting from the vanes. The unit might still be cooling a bit, but this one does damage quickly, so it jumps the queue. It is almost always a blocked drain or a coil so dirty the water cannot run off it.

Turn it off and leave it off. Running it wet just puts more water into your wall. This one needs a proper clean, not a check.

Where it stops being a you job

Be honest with yourself here, because the next steps are where people get hurt or wreck a unit trying to save a call.

• Anything electrical. Tripping, burning smell, the outdoor fan not turning, the unit not switching on at all. Stop resetting it. Every reset is another go at starting whatever is already failing.
• Refrigerant. This is the one people get wrong. Refrigerant is not fuel. It does not get used up, it does not need topping up every few years, and a unit that is “low on gas” has a leak. Finding the leak and fixing it is the job; just adding gas means you are back in six months with the same problem and less money. Handling refrigerant also needs an ARCtick licence by law, so this is never a DIY step.
• A dirty coil or barrel fan. You can see it, but you cannot reach it. The barrel fan sits behind the coil and takes a chemical clean under pressure with the unit bagged. Hosing the filters does nothing for it.
• It has not been looked at in years. Up here a split needs servicing at least every two years, ideally every year. If you cannot remember the last time, that is the answer to why it is not cooling, and a clean will do more for it than any repair.

When you ring

Have the make and model handy — it is on a sticker on the side of the indoor unit, or on the outdoor unit. Know roughly how old it is, and tell us which of the five above you have already checked. That alone usually tells us what to bring on the van.

And if there are kids, elderly people or anyone unwell in the house with no cooling in October, say so. It changes how fast we get there.