if the AC system is not operaated regularly the refrigerant will "settle" into areas of the system and it may take a few minutes for it to start circulating.
A freezing evaporator coil is sometimes a sign of low charge, or maybe insufficent air flow.
intermittently going from hot to cold may be AC clutch problems, "sticky" pressure switches, or maybe something simple like a loose electrical connection on a pressure switch or the power wires to the compressor clutch..
