nitro purge of mitsubushi bc box

[still learning]

just a question , if brazing a bc box where would you purge from to maintain a good flow of o f n , i have been told the flow thru a never powered up box is poor, is this correct ?
the fan coils are the flared type.

[stufus]

Purge form both main line connecting pipes and out at the indoor (fan coil flares)The flow of OFN can be negligible as you only need enough to displace the air at the point of the weld.
Cheers
Stu

[still learning]

thanks stufus.