Help please. Daikin u4 error

Outdoor unit- 4mxs32gvju

3 * indoor units- ctxs12hvju

A little backstory,

System has been in for 3 years, worked great for 2 years. Unit 1 in the bedroom started giving an occasional u4 error starting about a year ago. Cycling the system power usually fixed it. About 6 months ago the power cycle stopped helping and now it's always flashing led with u4 error. The other 2 indoor units have continued to work with no problems since installation.

The service monitor LEDs on the outdoor unit indicate all is normal there (flashing green with none of the Reds lit up).

I put a temporary communication line in (terminal 3) to make sure the line had continuity and it wasnt a wiring issue. No change.

All ac voltages on the outdoor units wiring terminals a-d are the same for each set. The dc voltage on the communication line for the 2 working indoor units fluctuates between 0v and 35v. The dc on the comm line for the unit that's not working and the terminals that are not hooked up are both at a constant 70v.

How do I determine whether it is the indoor pcb or outdoor pcb that needs to be replaced without an oscilloscope to check waveforms. Or is there any other tests I can run or checks I can do to make sure that I am replacing the correct part.

I am tempted to swap the pcb from one of my working indoor units but am concerned I may damage it if there is an issue with the outdoor pcb.

Any input or advice would be appreciated.

Thank you

You can safely swap out the pcbs to see if the fault moves without fear of damage. Power everything down before doing it

Well, I swapped the 2 of the indoor pcbs. And still get same u4 error in the same place. Clearly not the indoor pcb.

Anybody know the approx cost of an outdoor control board for a 4mxs32gvju in western Canada?

Thanks

Some Daikins had/have comms error where a faulty outdoor fan motor is taking the power down to the outdoor PCB.
Not sure about your setup but probably be worth powering the outdoor off for a couple of mins, unplug motor and power back up, see what happens.

Cheers,
Andy.

Quote:

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Originally Posted by Tayters

Some Daikins had/have comms error where a faulty outdoor fan motor is taking the power down to the outdoor PCB.
Not sure about your setup but probably be worth powering the outdoor off for a couple of mins, unplug motor and power back up, see what happens.

Cheers,
Andy.

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If it was the compressor fan would it not affect all the indoor units? I'll give it a go anyways. Doesn't hurt to try. Won't hurt anything powering up without the fan connected?

Thanks

The fan motor has a built in PCB which can fail and take the control voltage down across the outdoor unit. This would give you a dead outdoor PCB and a comms error. Don't forget the PCB's have a 240V supply but this is rectified and lowered to 5, 12, 15V DC to power up the various IC, temp probes, transducers, fan motor. Once you lose this then all a bit pear shaped.

This doesn't fit your case exactly as the monitor PCB lights up so you have some low voltage stuff kicking about, not sure but always gutting fitting a PCB and still have the same fault.

As long as you make sure unit has been powered down for a couple of minutes before unplugging fan you'll be fine. Motor has 340V on one of the pins which sparks across. Definitely need a fan and PCB then!

SOLVED!!!

No go on the fan tho taters, thanks anyway.

So dumb, I have an almost identical set up for the kitchen of my restaurant that won't be fired up for a couple of months yet. So I decided to swap the outdoor control boards. Took the bad one from mine took it to restaurant swapped it out. Lo and behold it worked fine at the restaurant. Totally confused, I brought the board from the restaurant home and went to install it in my home compressor.

While installing the restaurant board at the house I noticed the connector for the comm line of the problem unit was completely disconnected on the internal side of the terminal block. Reconnected it, installed board, everything is good.

Moral of the story, don't trust factory wiring and check all connections. It must have been really loose and worked its way off with the fan vibrations. That being said, I never would have noticed if I hadn't tried to swap those boards.

Thanks so much everyone for all the advice! So glad it didn't cost anything to fix but kinda upset at daikin quality control.

there is a app on android play store which you can download and it gives all the error codes. think its called daikin service