How are the efficiencies of AC or refrigeration systems affected by high ambient humidity?

The efficiencies of the system or systems will be greatly reduced. Because cooler air holds less moisture than warm air, the refrigeration system not only has to cool the air, but it has to dehumidify it at the same time. And since water vapor is condensed into water gives off a large amount of heat, there are times in humid areas where 70% or more of the systems capacity goes to removing moisture. That doesn't leave a lot for the actual cooling of the air.