daikin multi a/c shuts down u4 and a5

[2008_m_clarke]

hi i am having problems with my daikin a/con
it is a 4mk90hvec it is a multi-split system 4 indoor heads into the outdoor unit it has been working for years without a problem then the main room would only come on when you swithched it to fan and when you switch it to cool it shuts off this has been happening for a few months i am getting a u4 error code now the other remaining systems run for about a few hours then they shutt off they have recently been coming up with either u4 or a5 error codes the only way to get them working is shutting the power to the outdoor unit then back on then they work good for another hour or so i don't know a lot about these aircon systems the units have been thoroughly cleaned the led indicators on the outside pcb only one green flashing light that indicates no faults can anyone please help me thanks

[Meer Abdulrehma]

Hi

E3 means Transmission between indoor and outdoor units the F1 F2 connection terminals check maybe disconnected, wrong or cross wired or Short circuit. Good luck

[Meer Abdulrehma]

Sorry U4 means Transmission problem not E3 as above

[John Parr]

hi i am having problems with my daikin a/con
it is a 4mk90hvec it is a multi-split system 4 indoor heads into the outdoor unit it has been working for years without a problem then the main room would only come on when you swithched it to fan and when you switch it to cool it shuts off this has been happening for a few months i am getting a u4 error code now the other remaining systems run for about a few hours then they shutt off they have recently been coming up with either u4 or a5 error codes the only way to get them working is shutting the power to the outdoor unit then back on then they work good for another hour or so i don't know a lot about these aircon systems the units have been thoroughly cleaned the led indicators on the outside pcb only one green flashing light that indicates no faults can anyone please help me thanks
A U4 fault indicates a communication error between indoor and outdoor and or BS box, A5 is the temperature of the heat exchanger, this may indicate either a faulty sensor or refrigerant shortage, blocked capillaries , reversing valve malfunction (also gas related)

[VRVIII]

hi i am having problems with my daikin a/con
it is a 4mk90hvec it is a multi-split system 4 indoor heads into the outdoor unit it has been working for years without a problem then the main room would only come on when you swithched it to fan and when you switch it to cool it shuts off this has been happening for a few months i am getting a u4 error code now the other remaining systems run for about a few hours then they shutt off they have recently been coming up with either u4 or a5 error codes the only way to get them working is shutting the power to the outdoor unit then back on then they work good for another hour or so i don't know a lot about these aircon systems the units have been thoroughly cleaned the led indicators on the outside pcb only one green flashing light that indicates no faults can anyone please help me thanks
I would concentrate on the indoor with A5 and check following:

A5 error (Indoor freeze/overheat protection)

Supposed causes:

Wrong wiring or piping
Ev malfunctioning in each room
Short-circuit
Indoor unit heat exchanger temperature thermistor abnormality
Room temperature thermistor abnormality

[cool#9]

Hi clarke
Well in many cases i've had problem with these old units.
I recommend to check the outdoor pcb and search for some corrosion states on the components and on the printed areas, on the right side, at the A/B/C/D output / s10. see picture #773.
If you have u4 on A circuit ( for example ) try to change with another circuit which run well - you can do it on heating mode a few minutes -.
For a5 you maybe have overheating in heating mode or freeze-up routine in cooling mode, so checkout the filters, the fans, the dirt on the coils and as VRVIII said check also the wiring and the piping one by one... let's say there was a WIRING CORRECTOR button SW3 on the outdoor side ( see picture #769 ) to check the wiring at the first commissioning and then eliminate any wiring error but this will loose information after a power supply failure :rolleyes: so check it manualy one by one in cooling mode.
Good luck
cool#9

[Temprite]

Sounds like unit has 2 problems.

Unit is probably miswired which would explain A5 error.

PCB is getting old and corroded which will give you U4 error, usually on one head only.

This unit has a wiring correction switch on outdoor. Or alternatively reset unit and run one indoor unit at a time on cooling and see if any of the other units that are turned off have refrigerant flow by listening or feeling the coils with the filters removed.