Abstract: A plurality of temperature conditioning units are divided into groups with the groups being sequentially and repetitively, one after the other, enabled for a first preset number of timing intervals and then disabled for a second preset number of timing intervals. The sum of the first and second preset number of timing intervals is equal to the total number of groups so that at any given time, but on a rotating basis, the first preset number of groups of units is enabled and the second preset number is disabled. A setback feature which can be overriden by a thermostatic control is provided for off hours. An alarm system provides warning of abnormal operation of any one of the units as detected by excessive cycling.