Another thing to remember is the humidity levels. During this period, dendrobiums do not need a lot of moisture. Very little water will be enough to keep their roots alive. Also keep in mind that their roots constantly need plenty of air circulation so you should place them where there is a lot of fresh air.
Remember, that is based on energy usage, not comfort-levels, which are the purpose of having an air conditioner, in my not-so-humble opinion. Fact: At night, the ideal temperature comfort range for Americans drops to 65 to 72 degrees Fahrenheit (or about 87 degrees if you are my wife).
At standard design conditions, air coming out should be in the range of 55 to 60 degrees to cool the house down, regardless of the ambient house temperature. The unit should be able to cool even air at 85 degrees flowing into the unit down to 60 (at the vent) if it is functioning properly. Some factors that do influence the vent temp are where the unit is located, where the ducts are, how far the air has to travel, and the air speed.