Daikin U4 error code

I've been asked to look at a Daikin ducted unit model RYEP71L7V1 in an apartment block.

The initial problem was the indoor unit freezing up quite badly and causing considerable leaks in the ceiling void. Plus the remote displaying a U4 error code (comms problem?).

My client uses the apartment as a holiday home and therefore doesn't use the air conditioning much but did say the unit leaked water all the time.

After a process of elimination (there are about 20 outdoor units on the roof) I've discovered the outdoor unit doesn't switch off at all and so I think that may explain the ice build up.

I don't have any wiring diagrams but the power goes to the outdoor unit which then feeds the indoor unit.

The indoor unit will operate when the remote is switched on.

Any suggestions would be appreciated.

sounds like compressor relay welded closed if it's a conventional type (non inverter).
edit:
Daikin error codes here http://www.refrigeration-engineer.co...ghlight=daikin

You can download Daikin's full fault-code matrix HERE.

But...Outdoor unit is running constantly and there is a communication error, my suspicion is that the outdoor unit's PCB is gone..

check that the condenser relates to the evaporator your looking at - comms problems as well as freezing up / cooling all the time - could be mixed up interconnecting wiring, never swithching off due to another unit demanding the cooling process, from the wrong condenser. Is this a recent install?

is it possible the interconnects were mixed up?

U4 is an error in communication between indoor and outdoor units.

daikins have the "1,2,3" wiring, with off memory 1 is a premanent active, 2 being neutral, and 3 being a signal wire. if 1 and 3 were mixed up, would that possibly give a permanent active to the signal wire and possibly cause the condensor to continually run?

i dont know much about the internal workings of these units, just throwing something up in the air, some of the other guys on the forum will have a better idea.

No, because the outdoor gets mains voltage straight from the circuit breaker. If you swap '1' with '3' it's the indoor that would be only be getting signal, so it wouldn't be getting voltage to run.
Like I said, the outdoor unit is probably a pretty much melted mess, the relay contacts for the comp would be welded and the board itself pretty much fried.

if you switch the indoor unit off does the condensing unit stay running

Thanks for your suggestions.What I didn't mention was the unit is in Spain and fitted about three years ago by 'builders'. The wiring is literally open to the elements and my initial suspicion was that the indoor and outdoor units were incorrectly wired, especially when a brown wire ended up at a earth wire, but following it through, it does seem ok.

I cant confirm thats its ever worked, but judging by the ice, its been a long time.

Although my client left me the keys to his apartment, the 'President' of the urbanisation has changed keys to the front entrance and so I can't get back into the building until June....

Again, thankyou for your suggestions and I'm sorry it may take a while before I confirm what the problem was .

Hi, this might be too late but I think you will find the problem is that the outdoo runit has been switched into 'Emergancy' operation. This does two things; 1 The outdoor unit runs 24 hours 7 days, and 2 communication between the indoor and outdoor is stopped which is the U4 fault. The solution is to isolate the mains to the outdoor unit and switch DS1-1 to the off/down position and then turn the mains back on. Hope that helps.

what a noddy.