In need of a little help!

[gt82000]

Hello! I am hoping there is somebody out there has the wisdom i need to overcome the problem i am facing at the moment. Please speak in lamens terms as im mainly an install monkey! I know the basics of fault finding and that be that!
My friends dad is involved in a labour club and his Daikin multisplit has gone down with the code u4, transmission between indoor and out.
System is Daikin RY125FJ7W1, R22, 1998.
I have checked both main indoor boards and out. HP1 led is working on both indoor, HP2 is unlit, fuses ok. Checked outdoor board, power to it. All wiring between indoor and outdoor is ok. Is there a way of checking the other boards in the indoor units?
One of the indoor underslung's works on fan only the other doesn't which makes me think one of the other pcb's has gone. After 3 seconds as i change to heating/cooling U4 appears. They had a power cut 3 months ago, was wondering if this may have caused loss of address settings? If so does anybody know all the settings. Can anybody please point me in right direction? Once again, lamens terms please, u r talking to an install monkey!

[brunstar]

the unit you are looking at sounds like a twin split, if one unit works out of the two connected on fan only then it seems as though the printed circuit and or fan motor are faulty.
The reason it is coming up with U4 is because the communication between the second indoor and outdoor is not communicating. Usually this should come up with a U5 fault unless the outdoor printed circuit was damaged when they had the power problem.