Daikin RXS25F2V1B and RKS25F2V1B with error code U4

[Odden]

Trying to start my Daikin heatpump results in a blinking green led and the outdoor unit doesn't start at all. The wiring between in- and outdoor unit are correct and controlled.

Measuring the AC voltage on the indoor unit between 1 and 2 shows 230v, between 1 and 3 (comm) fluctuate around 86v and 2 and 3 fluctuate around 130v AC. The same at readings at the outdoor terminals. The green led on the outdoor unit is blinking and measuring the voltage on the outdoor pcb at the output of the rectifiers shows 26V DC.

At first, I thought the outdoor PCB was broken and changed it, but the same error code (U4) and the outdoor unit are still not working. Guess my readings on my multimeter should suspect something wrong with the inside pcb.

Anyone here who can guide me in the right direction?

[frank]

U4 is comms error. Either mis wiring or failed pcb.
Without power applied, can you do a continuity test on each wire to earth to confirm all is good. DC voltage with power applied should be measured between neutral and comms......NOT live and comms and should fluctuate up to 40v.
Are 1,2 and 3 terminals definately connected correctly indoor and outdoor? i.e. 1 to 1, 2 to 2 and 3 to 3.

[Odden]

U4 is comms error. Either mis wiring or failed pcb.
Without power applied, can you do a continuity test on each wire to earth to confirm all is good. DC voltage with power applied should be measured between neutral and comms......NOT live and comms and should fluctuate up to 40v.
Are 1,2 and 3 terminals definately connected correctly indoor and outdoor? i.e. 1 to 1, 2 to 2 and 3 to 3.

Thank's for your quick answer! Terminals 1 and 2 were twisted between outdoor/indoor.