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

[Kliimaseade]

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.

[Rob White]

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You say the valve is working, have you actually heard it move internally.
Try a solenoid magnet on the valves solenoid and see if it operates.
Try it a few times do not run the comp when trying but activate the valve
Manually a few times to prove the valves inards move.

Rob

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[Kliimaseade]

Thank You for the answer, Rob!

The valve itself works properly - when we disconnect the 4-way valve coil socket from PWB1 (contol PCB), the valve sets itself into "defrost" position. The same stuff with fan motor - it works all the time alongside compressor. On the first sight it is definitely the problem with PCB, but after replacement I have the same result. I think there is some kind of specific electronic problem with the unit.