Abstract: A space conditioning system for controlling the temperature and humidity of air within an enclosed space includes a vapor compression refrigeration unit having a reheat coil disposed downstream of the system evaporator coil to reheat return air after cooling and condensation of excess water vapor in the return air by the evaporator coil. The system includes a damper for controlling inflow of ambient outdoor air, depending on the total enthalpy of the outdoor air, so as to satisfy cooling and the dehumidification requirements without operating the refrigeration unit when the enthalpy of the outdoor air is suitable. The system includes a programmable controller for controlling air temperature and humidity within the enclosed space by sensing outdoor air enthalpy, temperature and humidity of air within the enclosed space and temperature or enthalpy of supply air being admitted to the enclosed space.