A frozen air conditioner is a common fault on humid summer days. Ice on an air conditioner’s indoor coil or pipes means the coil is running too cold. The usual reasons are too little airflow (dirty filters or a blocked return), low refrigerant from a leak, or running in cool mode on a cold night. Switch the unit to fan mode, or off, and let the ice melt completely before using it again. Clean the filters. If it freezes again with clean filters, book a technician.
Ice on the outdoor unit in heat mode during winter is different: that is normal frost, and the unit clears it with a defrost cycle. See reverse cycle not heating.
How to defrost it safely
- Switch to fan mode, or turn the unit off.
- Put a towel under the indoor unit. The melt water can overflow the drain tray.
- Wait until all the ice has gone. This can take an hour or more.
- Clean the filters while you wait.
- Never chip or scrape ice off the coil. The fins and pipes damage easily.
Causes and what each one needs
| Cause | What you’ll notice | DIY or technician |
|---|---|---|
| Dirty filters | Weak airflow; ice on the indoor coil | DIY |
| Fan set very low for long periods in humid weather | Ice builds overnight | DIY: raise the fan speed |
| Cooling on a cold night | Ice when outside is cool | DIY: use fan or dry mode instead |
| Dirty indoor coil or blower wheel | Ice returns with clean filters | Technician service |
| Low refrigerant (leak) | Ice on the thin pipe at the outdoor unit; weak cooling | Technician (ARCtick-licensed) |
| Faulty indoor fan motor or sensor | Fan slow or stopped; error code | Technician |
Why it leaks after freezing
When the ice melts, the water arrives faster than the drain can take it, and it spills from the front of the unit. If leaking continues after the ice has gone, the drain may be blocked too. See air conditioner leaking water.
If it keeps freezing, book a technician, or see split system regas and the troubleshooting hub.
In Australia, refrigerant work must be done by a technician who holds an ARC licence. You can read more about licensing on the ARCtick website.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles