Does A/C turn off automatically climbing hills ? Ford F53

It's not uncommon on the E series vans (at least those with the same v10 as the F53) to develop vacuum issues in the system that controls the ventilation "doors". My E350 has experienced that a couple of different times over the years...where at times the engine is under heavy load like climbing hills, the blower doors close, sending the air either to the defrost or nowhere. Sounds like what you might be experiencing.