Ductless systems are reliable, and when one stops cooling the cause is usually simpler than people expect. Start with the remote and the filters, then move to the parts that need a technician.
Check the remote first
- Mode. Make sure it is on COOL, not DRY, FAN, HEAT or AUTO. Dry mode runs gently to remove humidity and can feel like it is not cooling. Fan mode does not cool at all.
- Setpoint. Below the room temperature.
- Batteries. A weak remote may not send the change. Watch for the beep from the head when you press a button.
- Timers and eco modes that limit output.
- Multi-zone conflicts. On some multi-zone systems, if one head is set to heat and another to cool, the outdoor unit can only do one. The others wait or run fan only.
Clean the filters
Lift the front panel and slide out the mesh filters. If they are matted with dust, rinse them and let them dry. Dirty filters are the most common cause of weak cooling on mini-splits. See how to clean a mini-split.
Check the outdoor unit
- Is it running and is its fan spinning?
- Is the coil clean and clear of leaves, dust and cottonwood?
- Is there two to three feet of clearance around it?
- Is the breaker or disconnect on?
What needs a technician
A dirty blower wheel or coil
The squirrel-cage fan inside the head collects a sticky buildup that chokes airflow even with clean filters. Signs include weak airflow, black specks from the louvers and a musty smell. It needs a proper cleaning.
Low refrigerant
The most common cause of a mini-split that runs but blows only slightly cool air. Refrigerant is not consumed. On ductless systems the leak is often at a flare connection that was not made properly during installation. The fix is finding and repairing the leak, then evacuating and charging correctly, not just adding refrigerant. See refrigerant costs.
Ice on the coil or lines
A frozen coil from low airflow or low charge. Turn cooling off and run fan only until it thaws. See why an AC freezes.
Error codes
If the head shows flashing lights or an error code, it is reporting a fault such as a sensor, communication or pressure problem. See heat pump and mini-split light codes.
Undersized for the room
If the head has never kept up on hot afternoons, it may be too small for the room, common in converted garages and west-facing rooms. See what size mini-split you need.
A quick test
After fifteen minutes in cool mode, hold a thermometer at the head’s outlet and compare with room air. A healthy unit blows air noticeably colder, often in the range of 15 to 20 degrees below room temperature, depending on conditions. Much less points to airflow or refrigerant.
What we do
We clean the filters, coil and blower wheel as needed, leak test the flare connections, verify the charge by weight and pressure, and check the outdoor unit. Our diagnostic is a flat $69 and it is credited toward the repair. See mini-split leaking water and our ductless mini-split page.
Frequently asked questions
Why is my mini-split running but not cooling?
Common causes are the wrong mode on the remote, dirty filters, a dirty blower wheel or coil, a blocked outdoor unit, or low refrigerant from a leak.
Why is my mini-split blowing warm air?
Check that it is in COOL mode rather than FAN, DRY or HEAT. On multi-zone systems, another head set to heat can stop the others from cooling. If settings are right, the compressor may not be running or the charge may be low.
Does dry mode cool the room?
Somewhat, but it runs gently to remove humidity and may not lower the temperature much. Use COOL mode on hot days.
How do I know if my mini-split is low on refrigerant?
It runs but blows only slightly cool air, the coil may ice, and the room never reaches setpoint. A technician confirms it with pressure and temperature readings.
Why do mini-splits leak refrigerant?
Most often at flare connections that were not made or tightened correctly during installation.
Can a dirty mini-split stop cooling?
Yes. Dirty filters, coil or blower wheel choke airflow and cut cooling significantly.