New metal roof over old Asphalt shingle roof

I had a new metal roof installed a year ago in January 2019.
I had a leak in my roof before he installed the new roof. I asked him if he repaired the leak. He said he did not need to that he put a new roof over it. I thought that was an odd answer. But he is a professional and knows what he is talking about.
Six months later there was a spot in my bathroom at edge of the wall. And in the hallway a small rim damp around edge of wall by ceiling. About half an inch.
I called him and he came and looked and said no it was the ac unit.
I have a new unit. The new unit is a complete outdoor unit. I did not want it in the attic.
The spot went away. We had no rain. We had a lot of rain and the spot is back. He is supposed to come and check it.
Any advice on what to tell him. And about his response when I asked if they had repaired the roof before putting up new roof?
Please help!!
Thank you,
Cindy