Abstract: A system for conditioning air in a space by heating or cooling the air to change its temperature. A thermostat located within the space generates a two state temperature signal having a cyclic parameter which corresponds to the temperature of the air in the space as it rises and falls. A compressor supplies refrigerant to a heat exchanger by means of which changes are made in the temperature of the air. A variable speed motor drives the compressor in response to a motor control signal. A controller responds to the temperature signal and senses the cyclic parameter of the temperature signal. The controller generates the motor control signal as a function of the sensed cyclic parameter whereby the motor control signal is provided to the motor to control the torque or speed of the motor.

Abstract: A protective circuit arrangement for sheathed heating elements which interrupts ground fault conditions by effectively decoupling the power line from the heating element regardless of the polarity of the power supply connections. A fusible link couples each side of the heating element to the power supply. A normally open switch responsive to current in the ground path switches a relatively low resistance shunt current path across the heating element when the ground current exceeds a predetermined threshold level. Closure of the shunt path enables sufficient current to flow in the power supply lines to actuate the fusible links. Circuit parameters are selected such that the current in the fusible link coupled to the hot power line is sufficiently greater than that in the fusible link coupled to the neutral line to cause the hot power line fusible link to be actuated first, thereby interrupting the fault condition and decoupling the hot power line from the heating element.