Fault Code U4

Fault: Malfunction of transmission between indoor and outdoor unit
Short circuit in indoor-outdoor or outdoor-outdoor transmission wiring (F1 / F2), or wrong wiring
Outdoor unit power supply is OFF
System address does not match
Defective indoor unit PCB
Defective outdoor unit PCB
 

For Daikin split and multi-split air conditioning systems included wall-mounted, duct-connected, floor-standing, multi-flow, stylish, european, ururu sarara & cassette-type units.
If molded case circuit breakers or earth leakage circuit breakers have tripped, do not reset the breaker immediately without first checking for any problems with insulation of equipment.
Resetting breakers without a check of insulation may cause damage to equipment.