A programmable electronic digital thermostat provides improved control of a temperature conditioning system for varying load conditions in order to maintain the ambient temperature within a predefined range of a scheduled set temperature while minimizing ambient temperature overshoots and undershoots.

The fan coil unit includes an improved power supply circuit for simply and effectively providing its operating power utilizing an external alternating current power source of the temperature conditioning system and utilizing conventional existing wiring.

The zone valve includes a microprocessor for storing a program and for performing logical control operations in accordance with the stored program and a temperature sensing circuit that provides a pulse width modulated PWM signal representative of ambient temperature in response to an enable control signal from the microprocessor.