Daikin RZP100DV1 bottom fan won't spin and U2 error

[coldflow]

My dad has a Daikin RZP100DV1 Outdoor unit which is about 12years old. The lower fan won't spin when the AC is turned on and instead oscillates slightly back and fourth. If it is manually nudged it will start spinning and ramp up and down without issue. I have tried switching the top and bottom fan's connections at the PCB and the top fan will then start first without assistance but will then stop after a few seconds. This repeats a few times before the unit stops and a U2 error comes up on the remote. As the fan that won't spin unassisted was likely briefly submerged during floods we had a few years back, I decided to purchase a replacement fan from Daikin which initially worked well but is now giving the same error. I have found that if I disconnect power from the unit for a few hours that the new fan will start up without the error. If the unit has been switched off at the remote but still connected to mains for some time it will give the error. I'm guessing this behaviour maybe due to a difference in how warm the components are in the two scenarios.


I have reconnected the old fan and once nudged after turning on at the remote will keep spinning fine and the compressor will come on and cool or heat the house without any issues. The lower fan doesn't stop spinning until the unit is turned off at the remote even when the compressor has switched off (because the house has reached the set temperature) so doesn't need further nudging until the unit is turned off then back on again at the remote. The top fan spins up, down and off without any issue.


Reading around it sounds like possibly some sort of start / run capacitor associated with the bottom fan has failed and is giving this issue. I'm guessing as the bottom fan got damaged during the floods and is unable to start up itself, it doesn't drop the voltage in the system as much as the fans that can turn on unassisted.

I have inspected the PCB and there are no obviously visually faulty capacitors. There are 3 electrolytic caps (16V 120uF, 2 x 25V 100uF) as well as what looks like a polypropylene capacitor (blue rectangle 630VDC 0.1uF) that are associated with the bottom fan but not sure if they are the culprits. The top fan has its own identical set of 4 capacitors associated with it.


I don't have a multimeter that can measure capacitance and I'm not keen on randomly replacing caps as I'm worried I might end up converting a mostly working unit into a completely not working one!


Any advice?


Thanks in advance.