A device for controlling an HVAC system in which opening a door or window for more than a shutdown delay period causes the fan and compressor to be deactivated, but opening and closing the door or window for less than the shutdown delay period does not affect the fan and compressor. Reactivation of the compressor is delayed for a startup delay, in order to avoid overcycling of the compressor and the additional wear and tear and maintenance that would be caused thereby. Preferably, the door / window sensors are wireless for ease of installation and maintenance. Optionally, an occupancy sensor and occupancy timer are provided to turn off the system if the room is unoccupied for an unoccupied delay time. Optionally, a secondary thermostat with energy saving settings is provided so that if the room is unoccupied for the occupancy delay, then instead of being shut off, the HVAC system will be operated at energy saving settings.