Daikin U4? 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!

[Bartolo]

Hello!
you wrote that you've checked outdoor power supply, did you check led on the outdoor?

[gt82000]

yes checked led. green is constantly flashing, no red flashing or indication of fault. I know there is power there but could a swith/resistor possibly have gone on indoor or outdoor resulting in no signal and the board still appear to be fine?

[europa]

have you got power to both indoor units

[frank]

I have checked both main indoor boards and out. HP1 led is working on both indoor, HP2 is unlit

HP2 being unlit confirms that transmission is not taking place between indoor/outdoor.

Is the transmission wire taken through the high level float switch of the condensate pump?

Have you tried running a temporary single transmission wire between the indoor and outdoor units?

[gt82000]

Power is there (i guess, not tried yet!) due to HP1 led lit up on both indoor units. Gonna try runing a temp single transmission wire between indoor units on sat. cant get into units due to function nights.
FRANK... when u say run tranmission wire do u mean single cable from connection 2 or 3? I'm on the understanding from Daikin that there was 2 models of this system???
1 system had only 3 core cable and connection 2 is signal, or the other type is the system (which i have and to me is normal!) is 4 core, live, neutal, signal, earth. But i'm a bit dubious to the fact that 2 people i have spoken to from Daikin reckon its because of the power cut that i've lost adress setting???
I personally think it may well be one of the board's with no led's on it.
Gone over fault codes and you have a fault code for each of the indoor and outdoor PCB's so could it still be them?
Possibility of compressor? From memory whilst at college, if start and run windings dont add up to common, compressor is electrically goosed? Am i right in thinking this is done whilst power off? remember installation guy here!

[gt82000]

Not tried pump yet. Will look on Sat!

[gt82000]

And was working 2 months ago.

[frank]

Find out which is the transmission terminal (No.2 on the older units and No. 3 on the newer inverter units)

Run a single temporary wire from this terminal on the indoor unit to the same terminal on the outdoor unit and see if the HP2 starts to blink (unsteady flashing) Disconnect the existing transmission wire while you do this at both ends.

Power down before doing any wiring changes, and re-power when ready.

If the unit operates correctly with the temporary wire in situ, then the PCB's are OK and you need to look more closely at the existing transmission wiring for continuity.

A U4 fault has nothing to do with the compressor.

[gt82000]

Ran a single temporary transmission cable today and still nothing. But the funny thing was that the other unit wouldnt work on fan only until i had disconnected the single cable?
I have the led on the main pcb on the indoor that doesnt work flashing and the fuse is ok. Does this mean the board is stiil working? Is there a way of checking it?
There is also another small board with no fuse on. I think it has the relay on it. Is there any way of checking this board?

[El Padre]

Hi GT,

Power everything down swap the indoor boards and see if the fault stays with the same PCB, if so its faulty.

Cheers

[frank]

I've just re-read the first post. Is this a twin split installation? (2 indoor fan coils connected to 1 outdoor)

[gt82000]

yes it is a twin split.
I was a bit warry about swapping the boards over due to the fact if 1 pcb has blown for a reason it may blow another, then will have to pay for two pcb's.

[frank]

Did you run the temporary transmission wire between both indoor units and then to the outdoor?

Have you got HP1 and HP2 flashing on 1 cassette and only HP1 flashing on the other?

[El Padre]

You could try it with the fan motor unplugged and check the output from the board, also if you measure the voltage on the control signal terminal you don't have to worry about what the voltage is, just that its the same on both ends.

Have you checked the fan motors?

Cheers

[gt82000]

frank, no just ran from non working system, will run from both on next visit.
Thanks for that el padre, will also try.
will keep you posted.