Abstract: Precise control of the temperatures of leaving air in an air conditioning system and of leaving water in a water heating system are obtained with a throttling valve whose flow rate is modulated with an electric signal. The high pressure outlet of a refrigerant compressor is coupled jointly to the inlet of the valve and to the refrigerant inlet of a first condenser and the outlet of the valve is coupled jointly to the refrigerant outlet of the first condenser and to the refrigerant inlet of a second condenser. A programmable controller receives input signals corresponding to one or more entering media characteristics, such as dry bulb temperature, dew point temperature, and percent humidity and produces control signals that modulate the valve flow rate to thereby maintain the leaving air or water temperature at a specified set point with high precision.