Daikin VRV II U4 ( communitcation fault )

Evening gents from the land down under

First off love the forum , ive used it now a few times to gain some much needed infomation and has help alot.

However im stuck on some VRV II gear , Now im not asking for you guys to fix it but i really need to do some brain storming and gain some more angles to attack it from.

Story go ,

I have a multi story building and ive had a 3 Pipe branch box fail mechanically ( Blocked / Stuck solenoid valve ) on a floor , so ive been able to replace it. Now ive kept the same PCB installed however when power the floor back up i didnt have the B/Box connected to power so its come back with communication fault.

After realizing i re power it back up but this time it took the whole level out on a U4 fault , After some playing round i was able to get the floor back minus the unit ive been working on but the outdoor ( 1 master 1 slave ) its still stuck with a U4 fault and will not run

To date ive carried out a
- Reset of the condensers
- Removed the unit ( B/Box + evap ) out of the dasiy chain loop physically
- Tried codeing out the Master unit , incase it had a issue

But with no luck , this was a late afternoon issue so i didnt really have to time to get right in there.

My question is can you guy suggest some ideas and things to check , Voltages for the main PCB. i beleive its 18vdc ?

I dont know about your Daikin Tech but ours is a 1hr wait each time and im not the type of guy to be standing round playing with my self waiting for a call

Any help would be great , Cheers

So, to summarise, you had a perfectly working system until a 3 pipe BS Box failed. You have replaced the faulty BS Box and now you have a U4 comms fault that you can't clear.

It would seem that the fault is with either the F1 F2 wiring loop or the PCB that you saved from the faulty BS Box is faulty. Carefully check the F1 F2 indoor and outdoor wiring connections on the BS box you have replaced.

Using the binary's, can you see the correct number of indoor fan coils?

You say that you have done a reset on the outdoor 'Master' unit but still the U4 persists. Have you done a factory reset? Press and hold the 'Mode' button on the 'Master' for 20 seconds. This will reset the Outdoor pcb to factory condition and you will get a U3 fault, meaning that you must then carry out a Test operation.