Originally Posted by chchkiwi

I have never had a problem checking bags LAX-SYD-CHC on UA/NZ with separate tickets.

On the return trip, Air NZ most likely will not check your bags all the way through to the US. Make sure you have enough time between flights in SYD to clear immigration, collect your bags, go through customs then back upstairs to check in again. Last time I did this I waited one hour for the bags to appear on the carousel and almost missed the connecting flight. To be on the safe side, allow 2-1/2 - 3 hours.

Enjoy your trip!