New 2000 Eldorado owner with code questions

I bought a 2000 Eldorado a few days ago and it's throwing codes at me....
I have looked up the codes and seen the "definitions" but I am lost coming from a 1991 Mustang to this.
Here are my current codes not the history codes.......
P1545
P1585
B2502
I know they are A/C codes and a Trans shift lock ground but where do I start?
Thanks,
D