Buses and other similar vehicles for transporting a number of people are generally air conditioned to provide cooling on warm days. In addition, heating is provided to warm the interior of the vehicle when the days become cooler. With the advent of colder days, the relative humidity of the heated air inside the vehicle increases and the moisture in the air condenses upon the cooler surfaces of the vehicles, particularly the windows. This, in turn, makes it difficult for the driver to safely see out of the vehicle thereby producing a driving hazard. In addition, the atmosphere in the vehicle becomes ladened with moisture making the occupants uncomfortable.
Heretofore it has been the common practice on the part of the vehicle operator to turn on the air conditioning system when moisture builds up upon the windows in an effort to reduce the humidity in the air by cooling the air. However, running the air conditioning system when the ambient air temperature is relatively low places an unwanted load on the systems compressor which can lead to an early system failure. Additionally, the air conditioning cooling system is forced to work against the heating system as the air is being dehumidified thus resulting in a considerable waste of energy.