NIBE AMS10-8 / Mitsubishi Heavy Indutries FDCW71VNX-A deftrosting problem.

Good day to all.

Have a very interesting problem with NIBE AMS10-8 (NIBE Split 1) unit. Basically the same unit as Mitsubishi Heavy Indutries FDCW71VNX-A.

The unit does not make a defrost. On the indoor unit (ACVM10B-270/HMA100V1) display shows that the unit is in defrost mode, but actually the 4-way valve is "normal" mode (heating mode) and the fan is rotating - the voltage on both.

The 4-way vale is working - when it's socket is disassembled and the 4-way valve coil without voltage, valve itself in defrosting mode. The outdoor unit evaporator is full of ice. Outdoor unit understands that defrost should be done. The outdoor unit control PCB (PWB1) was replaced with a new one, dip switches are set correctly, but it does not help.

Does anyone has any experience with units like this? Thanks in advance.