daikin 4mk90hvec problems u4 a5 shutting down

[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 shutts 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

U4 -Malfunction of transmission between indoor and outdoor unit

[matt.yelland]

Hello

A9 = Electronic Expansion Valve Drive Error.. Check for power going to the EEV.

U4 = Comms fault between the Indoor and Outdoor unit..

All you are doing by switching the system off is making the unit run a diagnostic test on itself. When these faults come up again, you need to see what fault is coming up on the Condenser PCB

[VRVIII]

Hi,

A5 error = activation of indoor heat exchanger freeze protection (< 0 oC)

Checks;
1. Restriction or recirc of air flow (is the coil clean?)
2. Shortage of refrigerant
3. Coil thermistor out of calibration (check resistance/temp 10oC=40kOhms / 20=25kOhms / 25=20kOhms