u4 fault on a Daikin inverter

[phil17]

Got a U4 fault ( communication fault ) on a Daikin RZQ100B8V3B, R410 invertor. The strange thing is i have no led's lit up on the outside unit ( on either board). Both outside boards have been replaced , the wiring has been checked and the supply voltage ( 240volts ) has been checked but the fault persists. The indoor unit will run happily on fan only, and the indoor board appears ok ( green led flashing happily). Has anyone come acroos this fault before? Thanks

[Brian_UK]

Hi Phil, welcome to the forum and jump right in, I'm sure our Frank will have some input here.

[Temprite]

G'day Phil

Check that the outdoor fan is not seized. I have had faulty fan motors that have taken out boards before and caused U4 faults.

[frank]

According to the fault code list U4 refers to a break in communications between the indoor and outdoor PCB's.
The cause can be either on one of the boards or even the wiring between. If you put the comms wire through an isolator or over power cables in the ceiling void, this can introduce noise into the wire which disrupts the data flow and you get a U4 error code.

I always run a temporary seperate single core wire netween indoor and outdoor units to see if that solves the problem - if it does then you know the pcb's are OK and you need to investigate the wiring.

[phil17]

thanks for the reply Frank. Would a break in the inter connecting wiring cause all the led's on the outside board to go off? Even in fault i would have expected something to have been flashing a fault? We have got an indoor isolator and all the wiring through it has been checked and the terminals checked for tightness.

[frank]

Don't take the comms wire through the isolator! Make sure you crimp the wire straight through without a break. If you put the comms wire through the terminals in the isolator it can pick up noise from the mains passing at the side of it across the isolator terminal.

The lights on the outdoor board should be on. You should see a steady green flashing LED at about 5 hz which indicates the pcb is OK.

Try the temporary single comms wire to see if it is the wiring

[phil17]

sorry should have said; we are switching the live and neutral through the isolator and the '' switched live'' coming back is going through terminal block ( which i have checked). But we have no outside led's which is confusing every one and the reason why the outside boards got changed in the first place!

[Brian_UK]

Just a thought and I'm not 100% familiar with the unit but...

Is there a good neutral and is there a transformer powering the board that may be faulty?

[frank]

Has this unit ever worked or is this a new fault?

[phil17]

Have triple checked the power supply and its definitely 240 volts. There is no external transformer and both boards are brand new ( the old boards were less than three months old - new install)

[phil17]

Its worked for about three months

[frank]

Have a look at the attached wiring diagram. The power to the indoor control pcb (not the inverter board) is fed through a fuse. Is this OK?

[phil17]

have checked all the fuses on the outside boards and the surge arresters. The indoor unit runs happily on fan only

[LRAC]

The cause can be either on one of the boards or even the wiring between. If you put the comms wire through an isolator or over power cables in the ceiling void, this can introduce noise into the wire which disrupts the data flow and you get a U4 error code.

Hi Frank

I think we've all experienced that one at some stage, we always run seperate comms cables and not through an isolator.

Lrac

[puddleboy3]

This is a strange one!!! As you have said that the power is ok and the fact that the indoor unit is running (power for indoor supplied from outdoor) I would be looking more to the indoor unit PCB. A few questions is the system a single or twin? what is the model number of indoor fan coils? What is the history of the system did it just stop working or has the system been for instance pumped down and moved?

[Temprite]

I dont believe that the control wire is causing your U4 fault.

If it was open circuit you would still have LED's on the outdoor.

I believe your outdoor PCB's are faulty or you dont have power to them.

If the boards are faulty I would be checking for something that caused it.
eg compressor, fan motor.

Try taking the fan blade off and see if the shaft spins freely.

[freezy]

If you do not break the signal wire then someone can turn the isolator off to the indoor unit and there will still be a live into the unit.

Is this safe and installed to regs?

[Temprite]

I speak from experience.You can try it yuorself once and you'll see..............

Let me explain what i did :The interconnecting cable goes to the spur switch and i decided after a thousands of installs that i had to do some safe improvements and broke (1) and (3) live and signal but (2) neutral directly to indoor then guess what ********** U4 . I can bet my a** that it will show U4

Let me get this right....
Have not heard of a "spur switch" I presume you are talking about an isolator, but it sounds like you have it breaking the interconnects to the indoor unit.
If this is the case of course you will get a U4 fault because you are breaking the signal wire(3) and the outdoor unit still has power via line and neutral and as we all know Daikin units have the incoming mains connected to the outdoor unit.

From my neck of the woods any electrician that wires a Daikin only ever breaks the active to the outdoor unit all the interconnects(1),(2) and (3) go straight from the outdoor to the indoor without a break.

If you break signal wire(3) between the indoor and outdoor unit yes it will give you a U4 fault but you will still have LED'S on the outdoor. Breaking the signal wire will not cause the LED'S on the outdoor to dissapear,lack of power supply to the boards or faulty boards will cause the LED'S to not illuminate.

[Birds]

If you do not break the signal wire then someone can turn the isolator off to the indoor unit and there will still be a live into the unit.

Is this safe and installed to regs?

Is the signal wire fed from the indoor or outdoor unit?

Birds

[Daikin=Overated]

Have to agree with those pessimistic over this comms signal path being broken (or not). In my experience making no difference to diagnostic LED status or PC board health.

Besides..................

Fact of the matter is this. If your PCboard has no led's up what so ever, then you've either no voltage coming in to the board or a blown track on the flip side of the board (have you inspected this??). The connectors are colour coded, so theres little chance of putting things back the wrong way (Earth youself first, and allow PCboard to current drain before handling). This on the assumption that you've checked the fuses with a meter too-not just visual.

When you've life on the PC board, I.e LED's on the master PCB-central green LED's flashing, and extension PCboards to the left and right of master PCboard doing the same with a flashing green LED for healthy comms, then you'll need to do the following.
With the system powered down, isolate each indoor unit supply on the system. Isolate BC splitter box supply, then finally Isolate condenser supply. Leave for 20mins. Reinstate power to all the indoor units. Then turn all fixed wall controllers off.Reinstate power supply to BC Splitter box, and move on to the condenser. Reinstate power to condenser and immediately hold down the Reset surface mounted push button on the PCB (6th along to the right of the 7 master LED's). LED 2 will be flashing and LED 3 will be fixed at this stage.

The system does it's self diagnostic check, initiallises and then LED 2 extinguishes, with LED 3 fixed as before. System is now healthy and awaiting operation signal from controller.

Failing this get back to me, we'll go through the MODE funtion on the PCB which self teaches the system to identify all the indoor units again in the event of a complete system crash-high probability. The software is terrible, the logic get's confused over a power cut, and further more having to wait around for 20-30 mins for the PCboards to drain is uneceptable, and unpractical-especially when you've got three of these serving 15 indoor unit's like I had the other day, a shop that's freezing cold on all floors and a manager breathing down your neck, cos it's the third time it's happened this year. Again a prime example of an unnecessarily complicated approach to comms courtesy of Daikin. Rolls Royce of A/C they say, I'd have rather taken the 10 new Rollers I could have bought for the same price.

[adams?]

hi all, im new to this site and very impressed. this post caught my eye.
sounds like you have power problem. start by checking your supply to your outdoor pcb (connector Xsomthing but wiring diagram should show you). if no check any transformers etc. if yes first check fuse on board and replace if necseary. still no led's then get a new board. BEFORE you put the new board in check all electrical parts that connect to the board (fan motors etc. AND all wires) as it seems like somthing might be blowing up each new board as you fit it. also make sure nothing is touching back of board and all connectors are in the right place. if you get outdoor led's on and still get u4 then check your wiring.
good luck

[Obi Wan]

Hello Phil,

I would agree with most of the guys in that you have a power supply problem or that the Fan motor or the compressor is causing the problem.
See the attached drawing, disconnect the connectors marked in red. Check the power supply again. Check you get 230V AC between Live and N and also L to earth. Check N is not corssed with earth. Check the fuse on the main outdoor PCB is good. If the Green Led HAP still does not flash, replace the PCB. If this is the second PCB with the same problem then I would call the supplier and get them to come and take a look.

Daikin=Overated
Think you are talking about the wrong unit or system. Phil has a Sky Air inverter, You are talking about VRV. No wonder you get confused on the comms!!!!

[Daikin=Overated]

Hello Phil,



Daikin=Overated
Think you are talking about the wrong unit or system. Phil has a Sky Air inverter, You are talking about VRV. No wonder you get confused on the comms!!!!

Fair play and sorry for that. I missed the model number in question that time round.........had escaped me, having read through all the responses by the time of reply. However rest assure theres no confussion with Comms on my part. My point being directed towards Daikins overly complicated circuitry, as this post just exemplifies, if others are having similar difficulties on the more straight forward split system as opposed to the VRV as in my case. Still uses a varient of the same logic, albeit on a slightly smaller PCB arrangement minus the expansion boards still.

[phil17]

Hi Obi Wan, think i have checked everything you mention with the exception of a crossed neutral and earth ( not sure how much difference that would make if you were to chase the wires back to the supply source they join up anyway). I agree that something is killing the boards though. Our suppliers are coming out in the new year to have a play- and i wish them luck! This is a horrible problem!

[Obi Wan]

Fair play and sorry for that. I missed the model number in question that time round.........had escaped me, having read through all the responses by the time of reply. However rest assure theres no confussion with Comms on my part. My point being directed towards Daikins overly complicated circuitry, as this post just exemplifies, if others are having similar difficulties on the more straight forward split system as opposed to the VRV as in my case. Still uses a varient of the same logic, albeit on a slightly smaller PCB arrangement minus the expansion boards still.

Hello again,

I trust you had a good Xmas and are looking forward to the New Year.

I take our point at the complexity of the communications on the Daikin systems (splits, VRV, or otherwise). The designers at Daikin and other manufactures are responding to the changing nature of the refrigeration and air conditioning industry, some of which are self inflected through lack of training, skills and general poor quality of new engineers, while some are imposed by governments through legalisation in reducing global warming and not to mention the drive to make the systems more efficient.

When the first G series VRV was launched the communication were pretty simple, you just need to make sure you wired it correctly and commissioned it correctly. A lot of people had and still continue to have difficulty in understanding concept of polarity conscious wiring. And most did not understand the importance of the switch settings on the PCBs had they ever read the instructions manuals. Many new engineers cannot commission an A/C system in a systematic and logical manor. In order to maintain their dominant market share, Daikin had to engineer out such problems. In short, engineer out the engineers. E.g. to overcome silly field wiring mistakes they brought out the DIII net otherwise known as the F1,F2 super wiring system. Overall filed wiring was reduces by omitting one complete wiring loop and with non-polarity. As for the switch settings, a lot of this is now automated. The system adapts it’s self to your installation.
On the VRV II and III the you are obliged to perform a “test” function where the system will check you have opened the service valves, have not cross wired or piped the system, don’t have any blocked pipes or have not overcharged the system. Exactly the sort of thing the commissioning engineer should be checking.

In terms if the imposed changes, when the switchover to alternative refrigerants came about, dedicated indoor and outdoor units for R407C and R410A were created. This meant to stop misconnection of indoor outdoor units the communications had to carry out a “hand shake” between indoor and outdoor units to see if the two are compatible.
All of this cannot be achieved by just switching 230V. Communications of this type is necessary and has a big part to play. An A/C engineer now has to be a computer engineer to some degree. The same is the case in other fields, automotive industry, consumer white goods and telecommunications just to name a few. My grandfather was a car mechanic 30 years ago, he would be completely lost on a modern car. The modern A/C system have evolved, unfortunately engineers are struggling to keep up. The technical colleges are still teaching people on systems that were around 30 years ago.

So the point I am making is that it’s not the complexity of a system that is the problem but the ability of an individual to overcome a problem through their knowledge, skills, experience and by process of elimination or FTA (fault tree analysis). The manafactures are doing there bit to make the systems engineer proof.

Regards

Obi Wan

[sinewave]

Couldn't agree more Obi Wan!

[bryan]

un-plug the outdoor condenser fan motor off the inverter boardhen switch on and see if the green led starts to flash on pcb if it does fan motor had it,i`ve changed quite a few on the inverter condensing units.

HTH bryan

[bobkellyb]

XXX GOLD mmmmmmmmm

[bobkellyb]

G'Day
I have Daikin inverter ac's through my house, all interconnecting wiring is three core and earth (ecc)
It is the way they are designed to be connected!

Supply is connected to (1) + (2) 3 is the signal.
Unlike the earlier models where the signal was # 2
Also the earth has been moved to the oppisate
side of the terminal block.

[superswill]

i know iam coming in late on this one and have done very little with dakin but its not something as silly as the pump high level wired though the comms cable or remote?????

[puddleboy3]

Any update Phil17 have Daikin attended site to check out the problem?

[inverter]

do you have a condensate pump wired in line? Had loads of calls of this nature always been pumps?

[laf100]

Most Daikin outdoor boards do have an external transformer, 240v will come off the pcb to the TX then back to the board, check the wiring diagram to see if I am making it up or not! If there is one check the plugs are pushed on the board fully, I have also had bad connections in the plugs and dry joints o the boards of Daikin units. If there is no TX, then some Daikins have a small, concealed noise filter PCB befor the main board, that I have seen fail due to a power surge/spike. The outdoor board must have a flashing green led (HAP) before any comm's will take place, this is the case for all Daikin Pcb's. Keep us informed of how you are getting on mate.

[laf100]

Sorry Phil I am talking poop, just checked the wiring diags on Daikin website and there does not appear to be a transformer on the RZQ's, but there is the fuse F1U on the PCB, I have had these blow due to faulty outdoor fan motors or solenoid valves, lastly are the new pcb dip switches set up the same as the original board?

[momo]

Recently installed _MXS__E series from Daikin+...: power is supplied to the OUTDOOR unit which the supplies indoor units. The manufacturer designed the system this way: to modify it with isolators to indoor units without the manufacturers approval could lead to loss of guarantee. (USE WARNING LABELS: on indoor units for servicing etc indicating where the power isolator is)
Why ? You are using it in way that it was not designed for. You could get a faulty contact on an isolator messing up the voltages on the signal line which are referenced to either the Live or Neutral this would fry the signal circuits. If anything delay connection of the signal line after the L and N, but remember you must consider the signal line as being at mains voltage level. It is not a separate low voltage signal pair like KNX domotics or other serial comm. systems use.
About the MXS: goof proofed electrical side !!! Evidently Daiking knows that companies are using under-trained/competent labour (we can all make boo-boos - lets admit it ) and the unit will check whether your wiring corresponds to the pipes of the units connected .

[marc5180]

I came across a fault like this before christmas, the controller was flashing "U4" so i checked the comms cable, checked the outdoor pcb and it had no lights on it. Found the 2 stage fan to have a fault with it. It wasnt seized but for some reason it kept blowing the board. The fan didnt have a contactor or any sort of safety device to stop it blowing the board so when the fan failed it took out the PCB and also the transformer. I canged all three of these then problem solved.

[inverter]

Do you have aneon in the spur?

[phil17]

And the answer is..... the compressor was down to earth! Must have been the only thing we didnt check! Why it was blowing boards up and not tripping out the breaker im not sure. The boards themselves were unmarked, fuses and surge arrestor intact. Happily it was still under warranty, so at least we got a free compressor out of it You live and learn!

[Brian_UK]

Hi Phil, thanks for the update and it's good to know that the problem has been identified.

[dogma]

Lack of refrigeration....Add charge...after following codes....Then run test...