Daikin VRV U4 FAULT

[leegally1983]

It will be appreciated if any1 can help, i have two VRVs in the same area with 3 units on each system making 6 fan coils these all have seperate controls (wired) but one of which is the master control as the VRVs are two pipe systems. i keep getting a u4 fault on all the controls i have swapped the out door pcbs and they made no difference. Daikin tech have told me that there should be two master controls as there is two VRV condensers but if this is true why have the units ran for the last 4 years. i cant understand why both units are faulting with the same fault. some suggestions on what to check would be good also this fault started with JA and E3 faults on all the controls but without any work they have turned into this u4 fault
thanks

[acnerd]

I am used to the U4 fault being due to a loss of communication between indoor and outdoor units. Have you made sure that all indoor units are powered up and have a green LED flashing on their pcb's? Even one of them losing power, or switched off at a local isolator, will stop the whole system.

[marc5180]

What is the model number?
JA-Discharge side pressure sensor
E3- High pressure switch activated
u4- Transmission error

http://www.daikinac.com/commercial/d...SiUS39-601.pdf

Indoor to outdoor, outdoor to outdoor transmission wiring F1, F2 disconnection, short circuit or
wrong wiring
􀂄 Outdoor unit power supply is OFF
􀂄 System address doesn’t match
􀂄 Defect of indoor unit PC board
􀂄 Defect of outdoor unit PC board

[leegally1983]

I have checked all the above the indoors are running in fan only but the outdoor just never kicks in. Dont really understand the wiring on the indoors the control (master) is wired to the unit but not daisy chained to the other 5 units but the interconnecting is (f1-f2) even tho there is two out doors.

[majortom]

Check communication cables from outdoor to indoor units also check condenser fans. Could also be an indoor PCB failure or the new outdoor PCBs need to be reprogrammed to match system. Daikin can help with this.

[marc5180]

I have checked all the above the indoors are running in fan only but the outdoor just never kicks in. Dont really understand the wiring on the indoors the control (master) is wired to the unit but not daisy chained to the other 5 units but the interconnecting is (f1-f2) even tho there is two out doors.

What is the model number of the outdoor? Have you downloaded the service manual?

The service manual will give you a chart to follow to fix the problem.

[AbsoluteWDJ]

I would first start with checking your main 3 phase supply to each condensor.

[Bartolo]

Did You only change compressors on them or did You change PCB aswell? Try to just put them in test from the outdoor unit.
Are outdoor units pipe connected? If so than You have multi VRV system and it's normal that You have one master controller. Outdoor units schould be connected with Q1-Q2 and indoor units cabling schould be connected to F1-F2 in outdoor unit first on pipework from indoor units.

[Clk320_Greg]

TBh ive had this on systems before, i start with a full system reset and leave it 30 mins, more often then not itll come right. The daikin VRVs seem to be very sensertive and throw up fault codes for no real reason. i would say 70% of the time a reset sorts out comms errors!

[frank]

I have checked all the above the indoors are running in fan only but the outdoor just never kicks in. Dont really understand the wiring on the indoors the control (master) is wired to the unit but not daisy chained to the other 5 units but the interconnecting is (f1-f2) even tho there is two out doors.

In Fan Only, there will not be a call for the outdoor unit to run.
A U4 fault indicates that communication is lost between the indoor and outdoor pcb's. This could be caused by a number of different things, not least interference on the transmission wiring. Failed PCB's can be another cause.

[pushpendra]

Hi.can i know what to do? Daikin vrv2, model # RX10MY1, compressor #2 is grounded then i disconected the compressor terminal wire. Now i wan to run # 1 comressor only for test the control.but unit cnnot start. 1 no fcu sowing alarm cod u4 & ather fcu sowing j3. Thanks.

[SeyBrew]

In Fan Only, there will not be a call for the outdoor unit to run.
A U4 fault indicates that communication is lost between the indoor and outdoor pcb's. This could be caused by a number of different things, not least interference on the transmission wiring. Failed PCB's can be another cause.

Frank - I am hoping you are still around as I have just encountered a similar problem to the OP. I have had a power outage to the main plant room where all the outdoor units sit. This then caused a U4 failure across the board for these systems, which are now running on fan mode only.

We have re-set the outdoor units a few times and all the LED's are lit up, so it does not look like an outdoor PCB failure.

Any suggestions?

[frank]

Use logic in your fault finding.

When you have multiple systems on a site I always turn off all of the systems (indoor and outdoor) and then restart them 1 at a time, doing a hard reset each time.

Run each system up and if it settles and works, then switch it off and start the next one. This way, the faulty system causing the U4 error will show up, then you can concentrate your investigations a little closer, i.e. by swapping pcb's with known good ones until you find the culprit.

If your problem was caused by a power outage, I'll 99% certain suggest that 1 of your pcb's is fried.

[wozza]

I find it best splitting the system up.

e.g if you have ten indoors disconnect the F1-F2 from the fifth to the sixth and do a hard reset. Does the outdoor see all indoors? Does the system fault on U4? If it does fault on U4 then initate less units if it does not fault on U4 initiatemore units. It takes time but you normally get to the bottom of the problem.

[VRVIII]

I find it best splitting the system up.

e.g if you have ten indoors disconnect the F1-F2 from the fifth to the sixth and do a hard reset. Does the outdoor see all indoors? Does the system fault on U4? If it does fault on U4 then initate less units if it does not fault on U4 initiatemore units. It takes time but you normally get to the bottom of the problem.

Wonder where ya got these ideas from??