787 Air Cond Reset pushbutton

[BleedingOn]

I had a situation on 787 where neither engine would start. Neither start switch had any effect. The maintenance procedure called for the air cond reset pb to be pushed, but I’ve no idea why or what other function it has related to engine start. Could anybody shed any light?

[Fursty Ferret]

Never seen this before so can't offer more than a guess, but the same motor controllers used for engine start also handle the CACs. Perhaps there was a logic condition which was preventing the controllers disconnecting from the CACs and supplying the VFSGs on the engines, which was cleared by pushing the air con reset button? As I said, just a guess though.

[captain.ronin]

Never seen this before so can't offer more than a guess, but the same motor controllers used for engine start also handle the CACs. Perhaps there was a logic condition which was preventing the controllers disconnecting from the CACs and supplying the VFSGs on the engines, which was cleared by pushing the air con reset button? As I said, just a guess though.

That seems like a correct assumption. I have never seen this as part of an approved fault isolation procedure but it seems like a good way to correct such a scenario.