Are you sure that the coolant temp has nothing to do with AC system?
In fact for some newer model year vehicles,when the coolant temp is above the pre-set parameter, the ECM will shut off the AC.
I think the first thing should be done is to solve the overheating, then check AC.
From the descriptions given, I fully agree with biglow. Most likely is because a partially clogged radiator.
Good luck!
