Daikin FDQ250

Hello all. Today I had to commission a Daikin FDQ250 high velocity ducted unit. Prior to starting the unit I had concerns about the 230v power supply to the indoor unit, as this tapped off the 1, 2, 3 interconnecting cable to the L & N terminals (book says unit to have own 230v / 15amp supply), but Daikin tech confirmed that this isn't necessary and ok to tap off 1, 2, 3 from outdoor unit. Anyhow upon start checked the current draw of the indoor fan which was 8.5amp (data plate says 7.6mp), I was a little concerned as the power supply from outside is only a 6.3amp glass fuse off the outdoor board. After around an hour of operation and other checks, I walk back into the comms room to find a strong plasticky smell. I suspected the fan so check the amps which was now up to 10.5. Turned off the unit, remove the base panel to inspect the fan which extremely hot ( & the cause of the smell). The fan rotated freely with no resistance and there was no debris fouling the fan / impellers. I spoke to Daikin about the problem, checked winding resistance, connections etc, all ok. They asked about the ductwork design - there is none its just blows straight out of the spigots on the front down the room. They suggested that I should restrict the return air inlet, as there is no supply side duct to create air resistance. I duly blanked off 2/3 of the return air with some cardboard whilst monitoring the fan supply voltage and amperage. Immediately the fan amperage dropped from 10.5 to 4.5 amps, the voltage which was 225v increased to 230v. I settled on temporarily blanking 1/2 of the return air which saw the fan current settle at 6.5amp / 230v. Can anyone put some science to this? I was sceptical to their suggestion, but it worked, just want an explanation as to why.

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Some photos of the unit..

Fans are designed to operate against a certain resistance. That resistance requires a motor capable of providing the power to overcome the resistance.

If you remove the resistance then the airflow through the fan increases and requires more power.

Read up on the three fan laws and you will begin to understand the need for correct duct/fan design.

You need to put a trap in the drain on that model.

the more air the fans have to blow the more current they will pull