Daikin Mini-Split Not Cooling: Causes and Fixes
Quick Answer
When a Daikin mini-split is not cooling, the diagnosis depends on whether the outdoor unit compressor is running. If the indoor fan blows air but it is not cold, and the outdoor unit compressor is running, the most likely cause is low refrigerant charge - Daikin inverter compressors will continue running at reduced speed even with low charge, producing lukewarm air rather than shutting down immediately.
When a Daikin mini-split is not cooling, the diagnosis depends on whether the outdoor unit compressor is running. If the indoor fan blows air but it is not cold, and the outdoor unit compressor is running, the most likely cause is low refrigerant charge - Daikin inverter compressors will continue running at reduced speed even with low charge, producing lukewarm air rather than shutting down immediately. If the compressor is not running, check for error codes. The most DIY-friendly fix is cleaning the indoor filters and outdoor coil - restricted airflow on either side dramatically reduces cooling capacity. Daikin recommends cleaning indoor filters every 2 weeks during summer.
What Does the NOT-COOLING Code Mean?
Check if the outdoor compressor is running. If it is running but air is lukewarm, likely low refrigerant. If it is not running, check for error codes. Clean filters and outdoor coil first.
Most Likely Causes
Based on aggregated repair data, here is the probability breakdown for this error code:
Symptoms You May Notice
- Air blows from indoor unit but is not cold
- Cooling output weaker than usual
- Ice forming on indoor copper lines
- Outdoor unit running but not as loud as usual
- Room temperature not reaching setpoint
Can you reset a Daikin minisplit to clear the NOT-COOLING code?
Turn breaker off 30 seconds. After restart, set to COOL mode, lowest fan speed, and 5 degrees below room temperature. Allow 15 minutes for system to reach full capacity.
Tools Required for Diagnosis
Diagnostic Checklist
Follow these steps in order. We start with the easiest external fixes before opening up the machine.
Verify the remote is set to COOL mode (snowflake icon) and the
Verify the remote is set to COOL mode (snowflake icon) and the temperature setpoint is below room temperature. Check that the indoor unit is not in fan-only mode.
Remove and clean the indoor air filters
Go outside and check the outdoor unit
Replacement Parts
If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.
| Part Name | OEM Number | Estimated Price |
|---|---|---|
| Indoor air filter setModel-specific · $15–$30 | Model-specific | $15 – $30 |
| Coil cleanerN/A · $10–$20 | N/A | $10 – $20 |
Repair vs. Replace Calculator
Frequently Asked Questions
How cold should the air be from my Daikin?
My Daikin cools fine during the day but not at night. Why?
Can dirty filters really stop my Daikin from cooling?
Related Daikin Minisplit Error Codes
Models Known to Experience NOT-COOLING Errors
This repair applies to most Daikin minisplits with this error code. Common model numbers include:
FTXS09LVJU, FTXS12LVJU, FTXM15QVJU, FTXM18QVJU, FTXM24QVJU
Last verified for technical accuracy on March 15, 2026