This is a Digital Cycling Unit. It was installed as, Jim said, to control loads on the local utility in times of high demand. These were used mostly on Air conditioners.
Here is an excerpt from the manual for the unit.
What is a DCU? A Digital Cycling Unit (DCU) is a device installed at the home to control air conditioning units during a peak load period (as explained on page 3). The DCU receives radio signals from Utility and then begins to cycle the appliance. The device incorporates a circuit board, RF paging receiver, and transformer enclosed in a water-tight injection molded, high-impact poly-carbonate box and is usually installed near the air conditioner compressor. This device functions with central air conditioning systems and is not designed for window-style or small space units. The DCU responds to radio signals issued via an RF paging network – a network that communicates much like a cellular network. When The utility sees a system peak load approaching or when a system emergency occurs, it issues a signal over this network that tells the DCU to begin cycling participating units. Unlike some devices designed to completely turn the air conditioner off, Comverge’s DCU intelligently cycles the unit based on utility’s need so that the home remains cool while still reducing electrical demand. When the peak demand period ends, Utility will issue another signal that tells the units to gradually come back on line – one at a time in a random order – helping a utility to maintain safe and reliable service throughout a peak period. This gradual ramp-up function, called “cold load pickup” is pre-programmed into the unit and may activate whenever power is interrupted for more than 20 seconds. This may delay the units’ ramp-up by anywhere from 0 to 30 minutes.
Dan
