So I have a 95 F-250, and the air conditioning will only turn on if it is on before I turn on my Truck. Any suggestions on what this may be?

 

I don't know if this is the present problem, but if for example,
the magnetic clutch on the air conditioning compressor is not getting full power to provide a full engagement the clutch might be slipping when power is applied after starting. And yet if applied before starting it could be getting enough power to lock in and now will work until it is either stopped by choice or cooling requirement is satisfied.
That is only one possibility , there can be others.