daikin u4 fault

[davethefridge]

system details RZQ71B9V3B1 CONNECTED TO TWO FFQ35B8VIB Cassetts

Age 10 yrs

After about 8hrs running the system goes into U4 fault, when in U4 fault one of the fan coil fans runs.

service history no faults system serviced twice yr from new

When in fault LED lights on cassettes flash

Green LED GH HAP on condensing unit flashes

have disconnected terminal three from condensing unit and disconnected terminal three from both fan coil, there was a 1.9dcv on first fan coil and a 2.1dcv on fan coil two.

there is no external condense pump fitted to this system.

Help needed please

David

[Edit - thread moved from 'refrigerants' as it was not the topic of this post.]

[Brian_UK]

Have you checked the interconnecting wiring?

There may be a defective indoor pcb.

[al]

Is terminal 3 only connected on one indoor unit, not both? used to be the case on other brands.

[Keza]

I would also check the fan motor. Sometimes a faulty fan motor can cause a U4 fault.
Unplug it and start the unit, See if it runs ok for a little bit then it will fault out on fan motor missing fault. If U4 occurs then you may still have a faulty indoor PCB or interconnects