Complex sentence: Formerly, air conditioning was only in place in public rooms, such as the lobby, parlor and main dining room, but due to the nature of the building it was difficult to add air conditioning to all of the guest rooms.
Split into simpler sentences: Formerly, air conditioning was only available in public rooms, such as the lobby, parlor and main dining room. Due to the building's design it was difficult to add air conditioning to the guest rooms.