An improved monitoring and control system for a heating, ventilating and air conditioning (HVAC) unit which provides zone control in plural zones in which each zone includes a thermostat which controls a damper for its zone. One thermostat is selected and programmed to function as a monitor or master thermostat for selective actuation of the HVAC unit as well as controlling its zone damper. The other thermostats are programmed to function as slave thermostats and are interfaced with the master thermostat thereby allowing for independent zonal control in a multiple zone system which uses a single zone HVAC unit. The master thermostat may also receive control signals and data from higher intelligence such as a computer. Each thermostat is microcomputer-controlled with provision for both local and manufacturer programming via supplemental memory devices. The master thermostat contains a real time clock for time-basing the entire system with attendant advantages.