ErrorCodeDoctor
Daikin Air Conditioner U9 error code
The U9 error means your Daikin air conditioner detected a transmission fault between units in another connected system. This can be caused by a defective electronic expansion valve on another indoor unit, a defective indoor unit PCB, or an improper connection in the transmission wiring. Contact a qualified technician.
Common causes
- Transmission error between other indoor and outdoor units in the system
- Defective electronic expansion valve of another indoor unit
- Defective indoor unit PCB of another indoor unit
- Improper connection of transmission wiring
How to fix it
-
1
Contact a qualified technician to inspect the transmission wiring and expansion valves across all units in the system
Related Daikin Air Conditioner error codes
A0
An external protection device connected to the indoor unit has been activated
A1
A fault was detected in the indoor unit PCB (control board)
A3
The drain level control system has detected an abnormality — drain may be clogged
A5
Freeze-up protection (cooling) or high pressure control (heating) has activated — check the air filter
U9 error — frequently asked questions
What does the U9 error mean on a Daikin air conditioner?
A transmission fault was detected between other indoor and outdoor unit systems
What causes the U9 error?
The U9 error is usually caused by: Transmission error between other indoor and outdoor units in the system; Defective electronic expansion valve of another indoor unit; Defective indoor unit PCB of another indoor unit; Improper connection of transmission wiring.
Can I fix the U9 error myself?
This is rated a hard fix — it often requires tools, parts, or experience, and may be safer left to a professional technician.
How much does it cost to fix the U9 error?
Fixing the U9 error on a Daikin air conditioner typically costs $80–$350, depending on parts and whether you do it yourself or hire a technician.
Is it safe to keep using my air conditioner with the U9 error?
We'd recommend addressing the U9 error before continuing to use the air conditioner, since hard-rated issues often involve a real fault rather than a minor glitch.