The RS-PWIRE Phantom Wire™ device allows the installer to connect any Robertshaw Climate thermostat when a ‘common’ wire is not available in the existing thermostat cable.  This handy device ‘creates’ a phantom wire.  In many existing installations, older thermostat cables don’t have a common (24VAC common) wire because they were not needed for the mechanical thermostats originally installed.  Years ago, it was typical for the cable to only have four (4) conductors.  The RS-PWIRE creates the ‘common’ wire so the HVAC unit can be used along with any thermostat requiring a 24VAC common.  Additionally, the RS-PWIRE includes screwless terminals, color-coded wiring for the HVAC unit connection, and LEDs on the unit to show power, heat, cool and fan calls are being created from the thermostat, practically eliminating troubleshooting.