ErrorCodeDoctor
Daikin Air Conditioner U4 error code
The U4 error means your Daikin air conditioner detected a communication failure between the indoor and outdoor units. This is most commonly caused by a wiring fault in the indoor-outdoor transmission wiring (F1/F2), incorrect wiring, or the outdoor unit's power being off. Check that the outdoor unit is powered on and that the transmission wiring is correctly connected. Contact a qualified technician if the wiring is correct.
Common causes
- Short circuit or wrong wiring in the indoor-outdoor transmission wire (F1/F2)
- Outdoor unit power supply is off
- System address settings do not match
- Indoor unit PCB has a fault
- Outdoor unit PCB has a fault
How to fix it
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1
Check that the outdoor unit circuit breaker is on and the outdoor unit has power
-
2
Check that the F1/F2 transmission wiring between indoor and outdoor units is correctly and securely connected
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3
If wiring is correct and both units have power contact a qualified technician to inspect the PCBs and system address settings
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