Daikin Mini-Split Code C9
Warning
Room temperature thermistor or related abnormality. The sensor that reads room air temperature at the indoor unit is open or shorted.
Manual wording: “C9 Room temperature thermistor or related abnormality”
Documented for: FTXS-L, FDXS-L, H-Series, FTXM-W/V, RMXS indoor units
Likely causes, most common first
- Disconnection of connector
- Defective thermistor
- Defective indoor unit PCB
What you can safely check yourself
- Turn the system off at the breaker or disconnect switch and back on once
When to call a technician
C9 is a failed room sensor in the indoor unit. A technician has to check the connector and the thermistor's resistance value.
A Daikin mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Service Manual - Inverter Pair FTXS-L Series / FDXS-L Series (SiUS091133) (Daikin, FTXS09/12/15/18/24/30/36LVJU wall mount, FDXS09/12LVJU ducted, RKS/RXS09-36LVJU outdoor) · checked 2026-08-25
- Service Manual - Inverter Pair Wall Mounted Type H-Series (SiUS04-924_A) (Daikin, FTXS30/36HVJU indoor, RKS30/36HVJU and RXS30/36HVJU outdoor) · checked 2026-08-25
- Service Manual - Inverter Pair Wall Mounted Type FTXM-W/V Series (SiUS042113EA) (Daikin, FTXM-W / FTXM-V (Daikin Atmosphera) wall-mount heat pump) · checked 2026-08-25
- Service Manual - Multi-Split Type Air Conditioners RMXS-L Series (SiUS181631EA) (Daikin, RMXS48LVJU outdoor, BPMKS048A2U/049A3U branch provider, CTXG/CTXS/FTXS/CDXS/FDXS/FVXS/FFQ indoor units) · checked 2026-08-25