Daikin Multi Split blowing fuse

[Kirky]

Hi all had a call out yesterday to a Daikin RY200F7W1 multi split heat pump. Customer reported no power to unit. On arrival noticed all 4 cassettes not running and controller blank. At outdoor found that the L1 250V 10Amp fuse blown on outdoor pcb killing the power to the indoors. Checked isolator and found that seal had gone allowing water in. Replaced isolator and outdoor pcb for good measure. Reinstated power good supply to isolator 433 435 433v breaker stays in, so happy no short in wire from board to isolator. However when I turned on the isolator to energise the system the fuse blows as soon as I turn on. On the Pcb there are 2 fuses L1 and Neutral both 250v 10amp. L1 blows Neutral Ok. I have replaced cable from isolator to outdoor unit terminals so I know there isn't a short there. All wiring correct and no sign of any water ingress within unit. It seems to me that there is some other component causing the fuse to blow. Any ideas what. the fact that fuse blows immediately shows me it's a supply issue but supply all looks good. Any help welcome

[install monkey]

if ur blowing fuses on pcb then either outdoor fan- thermistors do short to earth q1h q2h i think
check crankcase heater as the rubber perishes and cooks itself to the pot, also the hp switch on smaller units can pop out the plastic clip and it shorts on the crimp terminals
unplug all safety circuits, hp,lp,comp overload fan thermistors then try it

[Mick13]

if it blows as soon as u turn the isolator on, i doubt its a fan motor. if i was in your position i would disconnect the 4 sets of interconnecting wires to your indoor units from the outdoor unit terminal block, replace the fuse then turn it on. if it doesnt blow, u know its in one of your indoor units, and if u wanted to u could reconnect them one by one to see which unit the problem lies with. my guess is it will be one of the indoor pcbs.

[Darrenp]

Check your fan motors and safety thermal cutouts , grey plugs , had this problem before found fan motors the problem !! Good luck :D