A sail switch for sensing air flow and responsively opening and closing a control circuit, the sail switch comprising a mounting base, a sail member, an arm supporting the sail member to the mounting base at a predetermined orientation thereto, an adjustable joint capable of varying orientation of the sail to the mounting base, and an electrical switch. The sail switch may have an orientation sensor and readout, a pilot light annunciating switch closure or opening, a time delay relay inhibiting control circuit shutdown, a thermostatic device monitoring air temperature, a communications feature transmitting sensed temperatures, an actuator for operating a supplementary cooling system, switch loading adjustability arranged to adjust force required to displace the sail member, a switch arm travel adjustment feature constraining range of travel of the sail member, a control circuit on-off switch, a transformer, a DC to AC inverter, and an AC to DC converter.