Daikin Air Conditioner C9 Error Code

Indoor room air temperature sensor fault on Daikin air conditioners.

May need a pro

The sensor reading the room air drawn into the indoor unit is giving an invalid value. A failed thermistor, a loose connection or the indoor board are the usual causes.

Compatible models

Daikin indoor units with a return-air sensor, which covers most of its range. Individual models aren't named.

Also shown as

Some Daikin listings use H9 for the outdoor air sensor, which is a different part.

Difficulty

Try the basic checks, but the usual fix is a technician's job.

How to fix
When to call a pro
Parts
FAQ

Not sure you are reading the code right? See how to read Daikin air conditioner codes.

Safety first: unplug the air conditioner (or switch off its breaker) before touching filters, hoses or panels. If you smell burning or gas, or see water near the outlet, stop and call a professional.

How to fix Daikin C9

One reset first
If the code stays after a breaker reset, the unit can't regulate room temperature properly until the sensor is replaced.
Record the code
Note C9 and the indoor unit's model number for the service call.

When to call a technician

Have an HVAC technician test and replace the room air thermistor or board.

Parts linked to C9

These are the parts most often behind this code. Tap one to see what it does and the signs it is failing.

Order parts by your full model number so they fit.

Frequently asked questions

Which Daikin models show the C9 code?

Daikin indoor units with a return-air sensor, which covers most of its range. Individual models aren't named.

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.

Other Daikin air conditioner codes

Last reviewed 2026-10-19. Codes and steps can vary by model; check your owner's manual.

Sources we checked