Home › Air Conditioners › Daikin › C9
Daikin Air Conditioner C9 Error Code
Indoor room air temperature sensor fault. Here is what it means and how to clear it, easiest fix first.
The sensor that reads the room air drawn into the indoor unit is giving an invalid reading. A failed thermistor, a loose connection or the indoor board are the usual causes.
Some Daikin listings use H9 for the outdoor air sensor, which is a different part. Daikin uses this code across its residential split, SkyAir and VRV ranges, but the exact meaning and causes can vary by series, model year and region, so confirm it in your unit's manual. How to read it: most Daikin ductless wall units only blink the operation lamp. On remotes such as the ARC433 series, press and hold the timer Cancel button for roughly 5 seconds until 00 blinks on the screen, then press Cancel again one step at a time; when the indoor unit answers with a long continuous beep, the code showing is the stored fault. SkyAir and VRV wireless remotes use a different sequence with the Inspection/Test, up/down and MODE buttons, and wired wall controllers usually show the code on their screen.
How to fix Daikin C9
Reset the power at the breaker
Switch the system off with the remote, then turn off its circuit breaker in your home's main panel. Wait about 5 minutes, switch the breaker back on and restart the unit. If the code stays, the unit can't regulate room temperature properly until the sensor is replaced.
Record the details for the technician
Write down the exact code, the model numbers from the labels on the indoor and outdoor units, and what the system was doing when the code appeared. Leave the unit switched off if the code keeps returning, so a fault doesn't cause further damage.
When to call a technician
Have an HVAC technician test and replace the room air thermistor or board.
Parts that commonly cause C9
- room air thermistor
- indoor control board
Order parts by your exact model number so they fit.
Other Daikin air conditioner codes
- U4Indoor and outdoor units can't communicate
- U0Low refrigerant or restricted refrigerant flow
- U2Power supply voltage problem
- UAIndoor and outdoor units don't match
- A1Indoor unit control board fault
- A3Condensate water level too high
- A5Freeze-up or overheat protection
- A6Indoor fan motor fault
- C4Indoor coil temperature sensor fault
- E1Outdoor unit control board fault
- E5Compressor overload or lock-up protection
- E6Compressor won't start
- E7Outdoor fan motor fault
- E8Compressor current too high
- F3Compressor discharge temperature too high
- F6High pressure in cooling mode
- H6Compressor position sensing error
- L4Inverter heat sink overheating
- L5Inverter output overcurrent
Frequently asked questions
What does C9 mean on a Daikin air conditioner?
The sensor that reads the room air drawn into the indoor unit is giving an invalid reading. A failed thermistor, a loose connection or the indoor board are the usual causes.
Can I fix Daikin C9 myself?
Only the basic checks. You can safely try the steps above, but C9 usually points to a part or fault that needs a technician.
What if C9 keeps coming back?
A code that returns after a reset and the checks above usually means a part is wearing out. Note when C9 appears (which cycle, how often) and have your model number ready; it helps a technician bring the right part on the first visit.
Last reviewed 2026-10-19. Codes and steps can vary by model; check your owner's manual.