Air conditioner not cooling? What to check before you call a technician

If your air conditioner is running but not cooling, the cause is usually something simple: a dirty filter, the wrong mode or temperature setting, or an outdoor unit that can’t get rid of heat. Check those first. If they’re all fine, the problem is more likely a low refrigerant charge, a frozen coil or a faulty part, and those need a licensed technician.

Six checks you can do yourself

Switch the unit off at the remote before you start, and don’t remove any panel other than the front cover and the filters.

1. Check the mode and temperature

Make sure the remote is set to cool (the snowflake symbol), not fan or dry. A simple test is to drop the set temperature to 16°C, and once you’ve confirmed cool air is coming out, set it back to about 22°C. Flat remote batteries can also make a unit seem to ignore your settings.

2. Clean the filters

Dirty filters are the most common reason for weak cooling. A clogged filter cuts the airflow, which also lowers the efficiency of the unit.

To clean them:

1. Turn the unit off and open the front panel.
2. Slide out the filters.
3. Shake off the dust outside, then wash them in warm soapy water if they’re grimy.
4. Let them dry completely before you put them back.

Clean the dust filters every few weeks, or every two weeks while the unit is in regular use, which suits Brisbane’s long cooling season. Even a lightly used unit needs it at least twice a year.

3. Look at the outdoor unit

The outdoor unit gets rid of the heat from your home, so a blocked one can’t do its job. Check that nothing is stacked against it, that plants and shrubs are trimmed back, that leaves, dust or cobwebs aren’t clogging the grille, and that the fan spins when the system runs.

An outdoor unit in full sun also has to work harder, so shade helps if you can provide it without blocking airflow.

4. Check the circuit breaker

If the indoor unit has no power or the outdoor unit isn’t starting, look at your switchboard. If the air conditioner’s breaker has tripped, switch it back on once.

If it trips again, leave it off and call a licensed electrician. A breaker that keeps tripping means an electrical fault or an overload, and resetting it again and again can make it worse. We’re both electricians and air conditioning technicians, so we can look at the wiring and the cooling in one visit.

5. Think about the weather

Air conditioners lose capacity as it gets hotter, and the drop starts once the outside temperature goes above 35°C. A good rule of thumb is to set the unit around 8°C cooler than the outside temperature, so a very low setting on a very hot day asks for more than the unit can give. If it struggles only during the hottest part of a heatwave and copes the rest of the time, it may be working normally.

6. Consider the size of the unit

A unit that’s too small for the room runs flat out and never catches up, especially on hot afternoons. If cooling has always been poor in one room, the unit may be undersized. See our guide to what size air conditioner you need.

Problems that need a technician

If those checks don’t fix it, these are the likely causes. None of them is a DIY job.

What you notice	Likely cause	Who fixes it
Warm air even on the correct settings, outdoor unit running	Low refrigerant (a leak) or a faulty compressor	Licensed technician
Ice on the pipes or indoor coil	Restricted airflow or low refrigerant	Technician, if the ice returns after you clean the filters
Water leaking inside	Blocked or badly sloped drain, or a frozen coil melting	Technician
Breaker keeps tripping	Electrical fault or overload	Licensed electrician
Loud grinding, banging or screeching	Failing fan motor or compressor	Technician
Musty smell that stays after cleaning the filters	Mould in the coil or drain	Technician

Low refrigerant

Refrigerant isn’t used up like fuel, so a low level means there is a leak. Topping it up without finding and fixing the leak only delays the problem. By law, anyone who handles refrigerant must hold a refrigerant handling licence, so this work isn’t something to attempt yourself or hand to someone unlicensed.

Ice on the coil

If you see ice on the indoor unit or the pipes, turn the system off and let it thaw completely. Clean the filters before you restart it. If ice forms again, the cause is deeper, such as low refrigerant.

Water leaks

Some condensation is normal, but pooling water is a problem and a safety risk. Water and electricity are a poor combination, so leave the troubleshooting to a specialist. Turn the unit off at the power point and call a technician.

When to replace instead of repair

Age and cost decide it. If the unit is more than about 10 years old, needs a major repair such as a new compressor, and your power bills have been climbing, a newer inverter model may cost less over the next few years. A technician can tell you what the repair would cost and whether it’s worth it. Our split system cost guide shows what a replacement typically costs.

How to avoid the problem next time

Clean the filters regularly through summer, keep the outdoor unit clear and trimmed back, and book a service by a licensed technician before the hot weather starts, in between your own cleaning.

Need it fixed?

We repair and service split systems across Brisbane’s south and south-west. We hold both an electrical licence (90313) and a refrigerant handling licence (ARC L142566), so we can find the fault whether it’s in the cooling or the wiring. Tell us the make and model and what you’ve noticed.

See our air conditioner repair and servicing, or call us on 0412 229 069.