provided at the heat cool select circuit the cool ramp circuit is disabled and only the temperature of sensor r 9 rising above the temperature of sensor r 11 will affect motor speed the sensor r 9 temperature when below the sensor r 11 temperature will maintain the heat cool ramp gen circuit at its minimum voltage motor 32 will either then be at zero speed or a minimum speed depending on the selection of the connection of jumper jp 1 for cutoff or minimum speed the heat input side of the heat cool select circuit includes capacitor c 12 diodes d 12 d 13 and resistors r 41 and r 42 lastly the control system 20 includes a sensor protection circuit including resistors r 47 r 48 r 49 r 50 r 51 capacitors c 1 diode d 15 and amplifier u 4 a a positive input signal to amplifier u 4 a of the sensor protection circuit is provided by the ramp output voltage signal and the protection circuit negative input to amplifier u 4 a is connected to a reference voltage available from resistors r 49 and r 50 when the ramp output voltage exceeds the reference voltage the output signal of amplifier u 4 a goes high and this dc voltage signal is connected to the opto isolator u 3 through diode d 15 this action causes the triac q 1 to be on full at all times and avoid the possibility of motor lockup still further there are three ways for the ramp output voltage signal to exceed the reference voltage signal at amplifier u 4 a which reference is established by resistors r 49.