We recently installed several Fujitsu cassettes. All run ok except one. It is showing a comms fault. We checked the cable with a meter, ok. We also disconnected our condensate pump.

Climate Centers AC tech said it must be outdoor board, changed it but fault still there. They then said it must be indoor board, changed it, fault still there. They suggested not wiring the neutral through the isolator but direct, did this, fault still there. (we had this fault on another Fujitsu unit and wiring the neutral directly eliminated the fault).

We're stuck, they're stuck. Can anyone help. Model numbers are, Cassette AUY12MAKL, outdoor unit AOY12MAKL