Why is my air conditioner not cooling? Causes and what to do
Most poor-cooling complaints come down to restricted airflow, and that is exactly what we inspect and resolve. Blocked filters, a loaded coil and a contaminated blower wheel all reduce cooling long before anything mechanical is at fault. Here is how to work through it, and how we diagnose it properly on site.
Quick checks first
Obvious, but worth two minutes. A surprising number of callouts are a unit left in fan mode or a set point above room temperature.
Airflow problems that cleaning resolves
An air conditioner cools by moving room air across a cold coil. Less air moving means less heat carried away, so the system runs longer and never quite gets there. These are the causes within our scope.
Blocked or collapsed filters
The first thing to check and the easiest to fix. A loaded filter chokes airflow immediately. A distorted one lets air bypass around the edges, which sends dust straight onto the coil.
A soiled evaporator coil
Material packed between the fins restricts air passing through, and also insulates the coil surface so it exchanges heat less effectively. In bad cases airflow drops enough that the coil ices up, which restricts it further and can lead to water overflowing the pan. See air conditioner leaking water.
Build-up on the blower wheel
Material packed into the fan blades changes their profile, so the fan physically cannot move the air it was designed to. This one is invisible from the front and is often the reason a system with clean filters still feels weak. See why cleaning your air conditioner filter isn’t enough.
Blocked returns, vents or registers
On ducted systems, a blocked return air filter starves the whole system, which is one reason ducted system cleaning works through the return, coil and supply side rather than the indoor unit alone. Closed-off registers, furniture over a vent, or crushed flexible ducting all reduce delivery to the rooms that need it. Worth walking the house and checking every outlet is actually blowing.
A blocked outdoor coil
The outdoor unit rejects the heat your system removes from the house. Smothered in leaves, grass clippings or garden growth, it can’t do that, and cooling capacity drops across the whole system. Give it half a metre clear on all sides.
Causes outside the airflow system
A smaller number of cases sit on the refrigeration side rather than the airflow side. We identify these during our assessment so you know exactly what you are dealing with before spending anything.
Systems don’t consume refrigerant, so low charge means a leak. Signs include icing on the pipework, poor cooling that got gradually worse over a season, and sometimes a faint sweet smell.
The outdoor unit humming without starting, or starting then stopping quickly, points here.
Intermittent operation, unresponsive controls or error codes on the display.
The system misreads temperature and cycles wrongly, often cooling briefly then stopping while the room is still warm.
If it has never coped on hot days since installation, no clean or repair will change that. It’s a capacity problem.
If it won’t run at all
Different problem, and worth working through before assuming the worst. If dust is coming out of the vents alongside poor cooling, an air conditioner blowing dust covers that pattern specifically.
A system that will not run at all is a supply or component issue rather than a hygiene one. If power, remote and settings all check out, tell us what it is doing and we will point you in the right direction.
Telling airflow from mechanical
Hold your hand at the outlet. If the air coming out is properly cold but there isn’t much of it, that’s an airflow problem, and cleaning is likely to help. If there’s plenty of air but it isn’t cold, the refrigeration side is the area to look at rather than the airflow side.
Two more signals. Gradual decline across a season or two suggests contamination building up. A sudden change from working fine to not cooling at all suggests a component or refrigerant fault. Ice on the indoor coil can be either, so it’s worth having looked at.
Not sure which one you’ve got?
Describe what your system is doing and we’ll tell you what we think is causing it. We assess airflow, coil and drain condition properly before recommending any work.
What we check on arrival
We run the system and measure the temperature difference between the air going into the unit and the air coming out, check airflow at the outlet, inspect the coil, fan and filters, and check the drain is clearing. That’s usually enough to establish whether the problem is contamination or something else.
If it’s contamination, we clean it and you’ll feel the difference immediately. For a wall-mounted unit that means a full split system clean. If our assessment shows the cause lies elsewhere, we tell you what we found and what to do next, rather than charging you for a clean that wouldn’t have fixed it.
Preventing it happening again
Filters every two to four weeks in season, the outdoor unit kept clear, and a full clean every six to twelve months depending on use. Airflow decline is gradual and mostly preventable, which is what how often should you clean your air conditioner is about. If you’re also seeing dust from the vents, why is my air conditioner blowing dust covers that.
Common questions
Why is my air conditioner running but not cooling?
If the air is cold but there isn’t much of it, that’s restricted airflow from the filters, coil or blower wheel, and a proper clean resolves it. If there’s plenty of air but it isn’t cold, the refrigeration side is the area to investigate instead.
Can a dirty filter really stop it cooling?
A heavily loaded filter reduces airflow enough to make a noticeable difference, and in bad cases contributes to the coil icing up, which stops cooling entirely. It’s the cheapest thing to rule out first.
Why does it cool for a while then stop?
Often icing: the coil gradually freezes as it runs, airflow drops to nothing, then it recovers once it defrosts. Restricted airflow from a loaded filter, coil or fan is a common contributor and sits squarely within cleaning. Low refrigerant is another possibility and sits outside it. It can also be a faulty sensor cycling the system wrongly.
Is this a cleaning issue or something else?
Cold air but weak flow, or a gradual decline across seasons, points to airflow restriction and starts with a clean. A sudden failure, plenty of air that isn’t cold, or ice on the pipework points elsewhere. Describe what it’s doing and we’ll tell you which it is before you spend anything.
Why is the indoor unit icing up?
Usually too little warm air passing over the coil, from blocked filters or heavy build-up, which is exactly what we clear. Less commonly it’s a refrigeration-side issue. Switch the system off and let it defrost fully before running it again, then have the airflow side checked first, since that’s the more likely cause.
My system won’t turn on at all. Can you help?
Check the isolator, the breaker and the remote batteries first, since those cover a fair proportion of cases. If it still won’t start, that’s a supply or component issue rather than a hygiene one. Tell us what it’s doing and we’ll point you in the right direction.
This article is general information, not advice for your specific system. Every make and model differs, so check your manufacturer’s handbook before carrying out any maintenance yourself. If you are not confident at any point, stop and have the work done professionally. Spotless Clean Air Services accepts no responsibility for damage or injury arising from work carried out by the reader.
Spotless Clean Air Services holds a Certificate II in Air Conditioning Hygiene accreditation. Airflow restriction is the most common and most fixable cause of poor cooling, and it is what we assess and resolve on every job.