Daikin u4 fault - please help!

[pie man]

Hello Engineers,

Back again was hoping some one might be able to help me out on this problem...my head is mashed!

I went to a site after an engineer had been the previous week, on controller showing U0 fault, checked unit was running LP 10-20PSI and low HP. Also noticed major icing up of suction pipe back to compressor. So thought low on gas, recovered and was short by 2kg, found a leak on the suction flare nut for the first fan coil unit, tightened up (there are two fan coil ducted units piped to one twin outdoor unit). Pressure tested to 300psi, went back today to check no leaks, vacced out and recharged to correct amount.

So happy days I thought this will be ok....Ran unit up again, now a U4 fault showing on controller, same readings very low suction pressure and h/p not too clever either - the charge is spot so added a little bit more but no effect (by the way using reclaimed R22 so not cheap!)

First I noticed the outdoor runs straight away... fans, compressor even though I havn't switched on controller inside room.
Switch the controller on in cooling, first indoor fan coil cools fine down to 11 degrees air off but go to second fan coil the fan motor aint running, no airflow :confused:.

So do I have a indoor to outdoor fault or a PCB indoor or outdoor failure? What tests do I need to do?

Model details are: outdoor RY250F7W1 / indoor FHYB125.

Thanks for reading, kind regards

Pie man :)

[kvas]

A year before i had the same problem (u4) and was burnt power poard or main board i dont remember. Try to reset your system from power and look if every led on your board is lit, and your fuses on main board is ok. (When i replaced burnt fuses, burnt immediately when re-power the unit.
Did you test your compressor if winding is ok?
If nothing, Take a look at communication cable s1,s2,s3 if there is a problem there, if terminals are tight.

[frank]

take a look at communication cable s1,s2,s3 if there is a problem there, if terminals are tight.
On a Daikin unit????

Sounds to me that the second indoor unit has a pcb problem - no comms and no fan running - causing the U4 fault

[Improver]

The second indoor unit p.c.b sounds faulty to me too but I have had a U4 fault code previously and I found that the condensate pump was the problem this was wired in to the S terminals when pump failed it caused a u4 fault code.

[pie man]

Thanks for responses guys, I'm going back to site this morning let you know how it goes!

[brunstar]

if you have a U4 fault and the unit is running then you could have the emergency switch set on the outdoor printed circuit board.
If it is an RY250 and the unit runs straight away you could also have a fused contactor or relay that supplies the contactor from the board. see if the contactor de energises when you turn the power off.

[Mick13]

Yes, if the dip switch (i think its labelled SW1) which puts the unit into forced cooling.... if thats on u will end up getting a U4 fault.... i had a tech i work with work on a unit and put it into forced cooling on a friday.... and i returned on the monday to find it out on U4 fault (and a block of ice because it had ran all weekend!)

However if ur turning both units on and the second fan isnt running.... it sounds like that may be your cause.... its indoor board possibly.... hard to say without seeing it!

[pie man]

Yeah it was set on cool on the outdoor by previous engineer...now running sweet after recharge, all air off temps fine. Thanks for responses everyone