Daikin U4 fault

[SeyBrew]

Hello all,

I am fairly new here so please be gentle.

Having a problem with some Daikin VRV machines we are installing in a hotel. We have had the systems (indoor and outdoor) running without incident for about two months now but we suddenly had a power failure on our site which cut off the main plant-room where most (but not all) of the outdoor units live.

After the power came back all we see is the error code of 'u4' on all the remote controllers and none of the outdoor units will start up again.

The system that did not get cut off by the power cut was fine and is still running without problems.

We have tried shutting down all the units, all the remotes etc... to no avail, still get the U4 code and the machines will not run.

We have also tried 're-setting' the pcboards by depressing the re-set button by nothing helps, still the same situation. The LED's on the PC board all light up, all the fuses are fine and there is good power getting to the units now....we just can't get the bloody things to start up again.

Any help would be very much appreciated.

Thanks,
Seybrew

[james10]

u4 is a communication error to reset the outdoor board you need to press and hold reset on the master unit (led3 lit on outdoor pcb) whilst turning the power off then back on to the out door unit if this does not work then you need to check the supply and comms wiring it could well be the outdoor board that is faulty

[SeyBrew]

thanks james, will try that tomorrow morning. We hit re-set but only tapped it as per the manual. I will hold it down and then re-set the power and see if that works.

[lawrence1]

SeyBrew,
Had a u4 call today on a 5 year old Daikin wall split.
Remote control was set on AUTO.
Reset to Cool,,,,all good.
Maybe it's that simple for you?i hope,
easiest call i've done for a while,apart from the 2 snake in a damper motor duct last week.
Lawrie
Lawrie

[shimceltic]

SeyBrew,
Had a u4 call today on a 5 year old Daikin wall split.
Remote control was set on AUTO.
Reset to Cool,,,,all good.
Maybe it's that simple for you?i hope,
easiest call i've done for a while,apart from the 2 snake in a damper motor duct last week.
Lawrie
Lawrie

I had a u4 yesterday, had to dao a hard reset as mentioned here by holding reset and powering down outdoor and while still holding reset power back up. Then wait for h2p to stop flashing ( around 10 mins) once this has gone off or solid steart a new test so it can find all indoors.

[wozza]

You dont have to keep your finger on the reset button when powering down. If the isolator is further away than an arms length it is impossible.
Power down then power back up and then put your finger on the reset button for 30secs, some people say 5secs and some people say 15secs.
I find 30secs covers eveything

[james10]

You dont have to keep your finger on the reset button when powering down. If the isolator is further away than an arms length it is impossible.
Power down then power back up and then put your finger on the reset button for 30secs, some people say 5secs and some people say 15secs.
I find 30secs covers eveything
Legally it should be possible as an isolator has to be within arms reach of the unit but i see your point it would be nice to live in a perfect world:D

[SeyBrew]

Thanks for all the advice. We have managed to get the systems back up and running. Turns out it was a power issue. Some imbalance on the phases was causing the electronic protection to kick in and prevent start up. As soon as the power was sorted out, the units started up automatically.

[danair]

was the power fault detected at the outdoor unit or incoming power into the building? as i have a daikin reyq14 which i replaced a compressor on around a month ago which now has a u4 fault. thinking power problem could have bricked the old compressor. and is now interfering with indoors or buggard the pcb possibly?????