Mitsubishi pffy-p40vlem-e communications problems

We have recently taken over the maintenance of a building with 8 PURY-P350 outdoor units and a large number of PFFY-P**VLEM-E indoor floor mounted fan coils.

Recently our engineer was called to a problem with a condensate pump that had failed. He found that the installing contractor had wired the mains power neutral through the condensate pump high water level failsafe switch. Worse than this, the pump neutral was wired together with outgoing wire of the failsafe switch on the mains input terminals of the fan coil. The engineer believes that this may have caused a 'racing effect', where the neutral was being connected and disconnected rapidly to the main printed circuit board.

He replaced the faulty pump and for the moment has removed the failsafe from the circuit. Live and neutral are wired direct to the mains power input terminals. 240V is present and the M net bus circuit has a voltage of about 30Volts DC. Neither of the mains power or communications LED's light up. We have replaced the indoor unit printed circuit board, but still neither of the LED's will light up.

We have powered down the m net circuit, BC box and the outdoor unit, but again after reinstating the power and the re-initialising period the LED's still do not light up and the fan coil remains inactive.

Since the first problem 2 other fan coils have suffered the same fate.

No faults are being reported and the fan coils appear on the touch screen controller, but if we try to switch the fan coils on from there they show on for about a minute and then switch off again.

Any ideas as to what or where the problem could be?

I suspect the system memory has been corrupted and the system will need to be rebooted from scratch, but I cannot understand why the PCB mains power LED's do not light up. (The onboard fuses are ok).

had noise filters fail on ducted units

May be that the incorrectly wired neutral has damaged the leds

The fan motor may be damaged from the Neutral switching and may have damaged the new PCB. Try unplugging the fan motor and do a power reset. If you cut the link on CN4F and wire it through the normally closed contacts of the pump this will bring up a drain fault if the high level is activated on the pump.

Thanks for the replies, I am inclined to agree that the fan motor is damaged due to switching the neutral. I am not sure if there is a link CN4F, there is a CN31 with a straight through link, we tried removing it and left a unit in operation, but no faults appeared.

Back there today and will try the things suggested. I'll update you all laters

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Originally Posted by Refrigerologist

Thanks for the replies, I am inclined to agree that the fan motor is damaged due to switching the neutral. I am not sure if there is a link CN4F, there is a CN31 with a straight through link, we tried removing it and left a unit in operation, but no faults appeared.

Back there today and will try the things suggested. I'll update you all laters

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Yes CN31 should generate a drain fault if removed. I think because of the dead PCB it will not generate a fault until the problem is resolved and the FCU is turned on.

CN31 does indeed generate a drain fault if the link is removed. Turns out that the transformer primary windings were open circuit on 3 fan coils. Mistake on my part, I didn't see the transformer as it is hidden behind another panel in the electrics compartment. Also didn't spot on the wiring diagram that the transformer is not on board the PCB. Very silly boy, must do better .... this is what happens when you have loads of faults and are about to go on holiday for a week ..........

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Originally Posted by narkom

It means that M-net is OK but there is no power on indoor unit.
Have you checked the transformer "T" with connectors CNT@CN3T?
CNT(1)-(3)App.15 Ω
CN3T(1)-(3) App.4 Ω

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Completely missed this reply, had I seen it I would have saved myself about 3 hours of head scratching.

Thanks for the update, glad that you've resolved it.