A split system blowing warm air
My split system is running but the air is not cold. Is it out of gas?
Published 05/10/2026. Written by the Pristine Cooling team, Kalgoorlie.
A split system that is running but blowing warm air is usually not out of gas. Refrigerant sits in a sealed circuit, so it does not get used up the way fuel does. If a system is genuinely low, something has made a hole and the gas has escaped through it. That does happen. More often the cooling has gone for a simpler reason to do with airflow or with one part that has stopped working.
Out of gas is not how a split system works
A car uses fuel. An air conditioner does not use refrigerant. The gas goes round a closed loop, picking heat up inside and dropping it outside, over and over. The same gas does that for years.
So a system that is low on charge has lost it somewhere. There is a hole in it. That hole is the fault. The missing gas is the symptom.
That matters because it changes what you are buying. A top up buys you a few months. Finding the hole fixes the problem.
What it usually turns out to be
It often comes back to the filters. A split system cools by moving room air across a cold coil, so choke that airflow and less heat gets picked up. The air out of the vents is not as cold as it should be. Filters nobody has washed in a while will do it. So will an indoor coil that has gone furry behind the filters, which is the part people never see.
Then the outdoor unit, because that is where the heat has to go. If the coil is packed with dust or the air cannot get around it, the heat has nowhere to leave and the system keeps running while delivering less. Out here dust is the usual reason, which is covered in what happens when plant runs hotter than it was chosen for.
Another is the outdoor fan not turning. If the compressor is running and that fan is sitting still, nothing is rejecting heat. The unit will either deliver nothing useful or shut itself down to protect itself. A failed fan motor or its capacitor does that.
The one that fools people most is the indoor fan working while the compressor is not. Air comes out of the vents, which sounds like a unit that is running, but it is only moving room air about. If what you can feel is air at room temperature rather than air that is slightly cool, that is the likeliest answer.
Ice on the indoor coil stops the job completely. Once a coil has frozen over no air gets through it and nothing can be measured until it has thawed. The ice is the result of something else though, usually poor airflow or a low charge, so melting it and carrying on gets you back to the same morning a week later.
Then there are the ones where nothing has failed at all. A setpoint sitting above the room temperature. A unit left in fan only or in dry mode. A remote somebody has put into heating. An economy or quiet setting holding the compressor back.
On a reverse cycle unit, a reversing valve stuck part way across will blow warm in cooling mode as well. That one is a real fault rather than a setting.
What it looks like when the charge genuinely is low
A low charge has a shape to it. The cooling fades across a season rather than failing on one afternoon. Ice forms on the thin copper pipe running into the indoor unit. Sometimes it forms at one patch on the coil rather than evenly across it. Oil marks around a flare nut or a joint are worth a look too, because the oil travels round with the refrigerant and leaves a residue where it has been getting out.
The leaks themselves turn up in a short list of places. The flare connections at either end. The service valves. Pipework that has spent years rubbing or vibrating against something. Coils that have corroded through.
Why topping it up is money you spend twice
Worth being blunt about this one. If a system is low, it leaked. Put a fresh charge in without finding the hole and the same hole lets it out again on roughly the same timeline. You pay for the gas. Then you pay for it again.
There is a second cost that is less obvious. A system running short of charge is hard on the compressor. The gas coming back on the suction side is what cools the motor inside a sealed compressor. The oil that lubricates it travels round with the refrigerant. Short of gas, that motor runs hotter and gets less oil back. So the cheap option can take years off the one component you least want to replace.
What finding a leak actually involves
Nitrogen goes in under pressure and the system is left to see whether it holds. An electronic detector goes over the joints and the coil. Sometimes a dye goes in and the unit runs for a while before anyone comes back to look for where it has shown up.
Once the leak is repaired the system gets evacuated properly. Then the charge goes back in by weight, to the figure the manufacturer gives for that model and that pipe run, rather than being topped up until the gauges look about right. That distinction matters more than it sounds. A system a little over or a little under its proper charge runs worse than one that is correct.
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