I can't say how many times now that I've posted this in response to similar questions, but here goes again.

My experiences over the past 2 years have been this:

2 flights to Mexico (CUN), 1 paid 1st class, 1 upgraded. BOTH times was offered (did NOT ask) use of AC lounge. Neither of these flights was non-stop and I was offered AC use at DFW, STL,& MIA (no AC at PDX, my departure airport, and obviously, no AC at CUN).

1 flight to Caribbean (PLS), upgraded. Offered AC use at DFW & MIA, did not have to ask, again.

I am not even Gold (always just miss it!), so no status comes into play here. I have been offered the use of AC on every segment of each of these flights, spanning from 5/00-3/01. Both Mexico and the Caribbean are "supposedly" considered Domestic for AA and almost everyone that posts here insists that you can NOT use the AC lounges on these routes unless an AC member, but in my experiences that is just NOT true. Surely I can not be the only one who is receiving this service? I've never even asked to use the AC lounges, let alone tried to bribe my way in.

So, my advice would be to ask if it is not offered. The worst they can say in no......

(Incidentally, flew Hawaiian Air in June of this year, paid first class, and was offered use of Delta's lounge at both PDX and HNL. Not sure what their "official" policy is on this either.....)